Yeah, that's one of the texts I was referring to in Acts 7: the formal identification of the "Angel of Yhwh" as the speaker of Yhwh's "I" in Exodus 3 and a couple of other passages is indeed central to both Philo and Justin.
Moses, then, the blessed and faithful servant of God, declares that He who appeared to Abraham under the oak in Mamre is God, sent with the two angels in His company to judge Sodom by Another who remains ever in the supercelestial places, invisible to all men, holding personal intercourse with none, whom we believe to be Maker and Father of all things; for he speaks thus: 'God appeared to him under the oak in Mature, as he sat at his tent-door at noontide. And lifting up his eyes, he saw, and behold, three men stood before him; and when he saw them, he ran to meet them from the door of his tent; and he bowed himself toward the ground, and said;' "(and so on;) " 'Abraham gat up early in the morning to the place where he stood before the Lord: and he looked toward Sodom and Gomorrah, and toward the adjacent country, and beheld, and, lo, a flame went up from the earth, like the smoke of a furnace.'" And when I had made an end of quoting these words, I asked them if they had understood them. And they said they had understood them, but that the passages adduced brought forward no proof that there is any other God or Lord, or that the Holy Spirit says so, besides the Maker of all things.
Then I replied, "I shall attempt to persuade you, since you have understood the Scriptures,[of the truth] of what I say, that there is, and that there is said to be, another God and Lord subject to the Maker of all things; who is also called an Angel, because He announces to men whatsoever the Maker of all things--above whom there is no other God--wishes to announce to them." And quoting once more the previous passage, I asked Trypho, "Do you think that God appeared to Abraham under the oak in Mature, as the Scripture asserts?"
He said, "Assuredly."
"Was He one of those three," I said, "whom Abraham saw, and whom the Holy Spirit of prophecy describes as men?"
He said, "No; but God appeared to him, before the vision of the three. Then those three whom the Scripture calls men, were angels; two of them sent to destroy Sodom, and one to announce the joyful tidings to Sarah, that she would bear a son; for which cause he was sent, and having accomplished his errand, went away."
"How then," said I, "does the one of the three, who was in the tent, and who said, 'I shall return to thee hereafter, and Sarah shall have a son,' appear to have returned when Sarah had begotten a son, and to be there declared, by the prophetic word, God? But that you may clearly discern what I say, listen to the words expressly employed by Moses; they are these: 'And Sarah saw the son of Hagar the Egyptian bond-woman, whom she bore to Abraham, sporting with Isaac her son, and said to Abraham, Cast out this bond-woman and her son; for the son of this bond-woman shall not share the inheritance of my son Isaac. And the matter seemed very grievous in Abraham's sight, because of his son. But God said to Abraham, Let it not be grievous in thy sight because of the son, and because of the bond-woman. In all that Sarah hath said unto thee, hearken to her voice; for in Isaac shall thy seed be called.' Have you perceived, then, that He who said under the oak that He would return, since He knew it would be necessary to advise Abraham to do what Sarah wished him, came back as it is written; and is God, as the words declare, when they so speak: 'God said to Abraham, Let it not be grievous in thy sight because of the son, and because of the bond-woman?' " I inquired. And Trypho said, "Certainly; but you have not proved from this that there is another God besides Him who appeared to Abraham, and who also appeared to the other patriarchs and prophets. You have proved, however, that we were wrong in believing that the three who were in the tent with Abraham were all angels."
I replied again, "If I could not have proved to you from the Scriptures that one of those three is God, and is called Angel, because, as I already said, He brings messages to those to whom God the Maker of all things wishes[messages to be brought], then in regard to Him who appeared to Abraham on earth in human form in like manner as the two angels who came with Him, and who was God even before the creation of the world, it were reasonable for you to entertain the same belief as is entertained by the whole of your nation."
"Assuredly," he said, "for up to this moment this has been our belief."
Then I replied, "Reverting to the Scriptures, I shall endeavour to persuade you, that He who is said to have appeared to Abraham, and to Jacob, and to Moses, and who is called God, is distinct from Him who made all things,--numerically, I mean, not[distinct] in will. For I affirm that He has never at any time done anything which He who made the world--above whom there is no other God--has not wished Him both to do and to engage Himself with."
And Trypho said, "Prove now that this is the case, that we also may agree with you. For we do not understand you to affirm that He has done or said anything contrary to the will of the Maker of all things."
Then I said, "The Scripture just quoted by me will make this plain to you. It is thus: 'The sun was risen on the earth, and Lot entered into Segor(Zoar); and the Lord rained on Sodom sulphur and fire from the Lord out of heaven, and overthrew these cities and all the neighbourhood.' "
Then the fourth of those who had remained with Trypho said, "It must therefore necessarily be said that one of the two angels who went to Sodom, and is named by Moses in the Scripture Lord, is different from Him who also is God and appeared to Abraham."
"It is not on this ground solely," I said, "that it must be admitted absolutely that some other one is called Lord by the Holy Spirit besides Him who is considered Maker of all things; not solely[for what is said] by Moses, but also[for what is said] by David. For there is written by him: 'The Lord says to my Lord, Sit on My right hand, until I make Thine enemies Thy footstool,' as I have already quoted. And again, in other words: 'Thy throne, O God, is for ever and ever. A sceptre of equity is the sceptre of Thy kingdom: Thou hast loved righteousness and hated iniquity: therefore God, even Thy God, hath anointed Thee with the oil of gladness above Thy fellows.' If, therefore, you assert that the Holy Spirit calls some other one God and Lord, besides the Father of all things and His Christ, answer me; for I undertake to prove to you from Scriptures themselves, that He whom the Scripture calls Lord is not one of the two angels that went to Sodom, but He who was with them, and is called God, that appeared to Abraham."
And Trypho said, "Prove this; for, as you see, the day advances, and we are not prepared for such perilous replies; since never yet have we heard any man investigating, or searching into, or proving these matters; nor would we have tolerated your conversation, had you not referred everything to the Scriptures: for you are very zealous in adducing proofs from them; and you are of opinion that there is no God above the Maker of all things."
Then I replied, "You are aware, then, that the Scripture says, 'And the Lord said to Abraham, Why did Sarah hugh, saying, Shall I truly conceive? for I am old. Is anything impossible with God? At the time appointed shall I return to thee according to the time of life, and Sarah shall have a son.' And after a little interval: 'And the men rose up from thence, and looked towards Sodom and Gomorrah; and Abraham went with them, to bring them on the way. And the Lord said, I will not conceal from Abraham, my servant, what I do.' And again, after a little, it thus says: 'The Lord said, The cry of Sodom and Gomorrah is great, and their sins are very grievous. I will go down now, and see whether they have done altogether according to their cry which has come unto me; and if not, that I may know. And the men turned away thence, and went to Sodom. But Abraham was standing before the Lord; and Abraham drew near, and said, Wilt Thou destroy the righteous with the wicked?' "(and so on, for I do not think fit to write over again the same words, having written them all before, but shall of necessity give those by which I established the proof to Trypho and his companions. Then I proceeded to what follows, in which these words are recorded:) " 'And the Lord went His way as soon as He had left communing with Abraham; and[Abraham] went to his place. And there came two angels to Sodom at even. And Lot sat in the gate of Sodom;' and what follows until, 'But the men put forth their hands, and pulled Lot into the house to them, and shut to the door of the house;' and what follows till, 'And the angels laid hold on his hand, and on the hand of his wife, and on the hands of his daughters, the Lord being merciful to him. And it came to pass, when they had brought them forth abroad, that they said, Save, save thy life. Look not behind thee, nor stay in all the neighbourhood; escape to the mountain, lest thou be taken along with[them]. And Lot said to them, I beseech[Thee], O Lord, since Thy servant bath found grace in Thy sight, and Thou hast magnified Thy righteousness, which Thou showest towards me in saving my life; but I cannot escape to the mountain, lest evil overtake me, and I die. Behold, this city is near to flee unto, and it is small: there I shall be safe, since it is small; and any soul shall live. And He said to him, Behold, I have accepted thee also in this matter, so as not to destroy the city for which thou hast spoken. Make haste to save thyself there; for I shall not do anything till thou be come thither. Therefore he called the name of the city Segor(Zoar). The sun was risen upon the earth; and Lot entered into Segor(Zoar). And the Lord rained on Sodom and Gomorrah sulphur and fire from the Lord out of heaven; and He overthrew these cities, and all the neighbourhood.'" And after another pause I added: "And now have you not perceived, my friends, that one of the three, who is both God and Lord, and ministers to Him who is in the heavens, is Lord of the two angels? For when[the angels] proceeded to Sodom, He remained behind, and communed with Abraham in the words recorded by Moses; and when He departed after the conversation, Abraham went back to his place. And when he came[to Sodom], the two angels no longer conversed with Lot, but Himself, as the Scripture makes evident; and He is the Lord who received commission from the Lord who[remains] in the heavens, i.e.,the Maker of all things, to inflict upon Sodom and Gomorrah the[judgments] which the Scripture describes in these terms:'The Lord rained down upon Sodom and Gomorrah sulphur and fire from the Lord out of heaven.' "
