John chapter 1, opening verses, speaks of the one who was with God in the beginning, and who was God, and who made everything that was made. It then shows that this "Word became flesh and dwelt among us, and we beheld his glory, that of the only-begotten of the Father, full of grace and truth" (vs. 14).
As God the Father has no beginning, one who was with him and who was God could not have had any beginning either. Verse 3 confirms that without this one, nothing that was made was made. Logically, then, this one could not have been made himself. That is why he is called "God" by John, both here and at the end of his account - "My Lord and my God" - (20:28).
Philippians 2:9 (which you allude to but don't cite) is understood by those who have the Word as a creature (hence lower than God right from the start; not God) as becoming the man, Jesus, who could be exalted back to a certain level of glory after his resurrection. No problem, they think, except that such an interpretation utterly depends on the Word having a starting point in time, being created by God. They have John 1:1 say the Word was 'a god'.
But those who take John 1:1-14 as showing the uncreated status of the Word, see a far greater degree of abasement in that lowering. Then, at his resurrection, the Father exalted him from that abased position. This means that both groups agree on the sequence of events: initially exalted, abased, then exalted. The disagreement is regarding degree of initial exaltation, degree of abasement and degree of exaltation.
Those who believe the Word was God see God, in Christ, so identifying with humanity that they understand what doubting Thomas said (and felt) in John 20:28, whereas those who think it wasn't God in Christ just don't get it. Philippians 2:9 is couched in words of exhortation for Christians to have that same humility of mind. Further, it says that although he was in the form of God, he did not grasp on to that; He agreed to be made in the likeness of men and to suffer humiliating death, knowing the Father would exalt him.
The Father, Son, and Holy Spirit determined this plan of redemption before anything was created, which is why the Bible speaks of Christ as "the Lamb of God, slain from the foundation of the world" (Revelation 13:8). It was decreed and as good as done, for the Word of God is inviolable. That plan included exaltation of the one who abased himself, which is why it happened.