John testified about Him and cried out, saying, “This was He of whom I said, ‘He who comes after me has a higher rank than I, for He existed before me.'” John 1:15 (cf. 1:30)
The phrase translated as “existing before” is protos mou (πρῶτός μου). It is grammatically ambiguous, referring to either:
a. prior in time
b. higher in superiority
John 1:15 (1:30) could equally be translated: He who comes after me has a higher rank than I, for He was my superior. The same goes to John 1:30 where the phrase reappears. The Greek protos is similarly used in 1 Tim. 1:15 where Paul claims to be the “foremost” of all the sinners Jesus came to save.
In short, John 1:15 is an ambiguous text which can be made to refer to preexistence or to preeminence, depending on your presuppositions.