The doctrine about Christophany teaches that before the eternal Son was incarnated he already appeared in the Old Testament as the Angel of the Lord.
The question is if there is a New Testament backround about this.
Yes, before Jesus was born there was references to the Angel of the Lord. Take a look at Exodus 23:20
"See, I am sending an angel ahead of you to guard you along the way and to bring you to the place I have prepared."
You could say that Jesus protected the true Christians both spiritually and physically. It also refers to this angel bringing them to a place God prepared. This could be referring to Jesus's sacrifice opening the way to salvation for all men.
God also foreshadows more about this angel in the next verse of Exodus 23:21:
"Pay attention to him, and obey his voice. Do not rebel against him, for he will not pardon your transgressions, because my name is in him."
"because my name is in him". This could be referring to Jesus being a perfect reflection of his father. This could also be talking about the translation of Jesus's name.
"(Je′sus) [Lat. form of the Gr. I·e·sous′, which corresponds to the Heb. Ye·shu′aʽ or Yehoh·shu′aʽ and means “Jehovah Is Salvation”]."
These are all from the Old testament.
The new testament also has scripture that show Jesus was around even before man and the earth. Most people don't accept my bibles rendering of John 1:1&2, however it still shows that the Word or Jesus was around before the earth and even helped create it.
Here is another verse from John 1:14
"So the Word became flesh and resided among us, and we had a view of his glory, a glory such as belongs to an only-begotten son from a father; and he was full of divine favor and truth. 15 (John bore witness about him, yes, he cried out: “This was the one of whom I said, ‘The one coming behind me has advanced in front of me, for he existed before me.’”)
This same thought is reiterated later in Colossians 1:16. There are a few other scriptures, but I think this should cover it enough.