I cannot find a translation for the alleged assertion. Without a reference to base the alleged assertion, this question appears designed to draw out answers whether Jesus is God or not. Note too that the OP's question is testing his alleged conversation with a unitarian. What does alleging a unitarian adding the "a" would make it look like?
Given that the translation of Philippians 2:6 should be "who, being in the form of God, thought [it] not something to be seized to be equal to God", such a translation does not say that Jesus is God. To assert that it does it to force on Jesus what he refused, That is the opposite of what Philippians 2:6 is saying. The assertion that Jesus is God or is not God should be examined according to what the rest of the bible say and not take a verse in isolation and make it say what it does not say. Translations and interpretations “should not go beyond what is written.” 1 Corinthians 4:6
The bible does not show Jesus as the Creator, the almighty God, YHWH. Jesus himself ascribed creation to God not himself. Matthew 19:6, Jesus asked And he answering said to them, 'Did ye not read, that He who made them, from the beginning a male and a female made them, "Did ye not read" .There is nothing in the scriptures that Jesus quoted from that ascribes creation to him. Others cite John 1-1:3 and assert that Jesus is the Creator, but that would mean that there are two Creators/God.
Thus, in Jesus own words he cannot be the Creator God that he ascribes creation to. Others state God is one, yet equivocate the word one to include Jesus. But according to Jesus himself, he and the Father equals 2 witness, not 1 as John 8:17-18 show.
If one represents God as two Beings/Persons and divides one of those person, Jesus, by assigning to him a divine and human nature, consider the following.
How can Jesus be infinite and finite, omnipotent and needs strengthening, omniscient and yet ignorant of some things, the almighty Creator of the universe yet a baby laying in a manger, immortal and mortal at the same time. These are contradictory. These are qualities that are incompatible with each other.
Part of one respondent's answer reads,
when Deity is being spoken of, language must very precise indeed. It can be seen how careful John is in regard to the presence and absence of 'the' in John 1:1 :
εν αρχη ην ο λογος και ο λογος ην προς τον θεον και θεος ην ο λογος
In the beginning was the word and the word was with the Deity and Deity was the word.
In both John 1:1 and in the text before us (Philippians 2:6) the meaning is profoundly altered if one introduces an 'a' in front of the anarthrous Greek word θεος.
Examining the quoted part that respondent's answer and the verse cited, John 1:1, we have the word God mentioned twice.
If as this respondent has stated that "when Deity is being spoken of, language must very precise indeed." in order to be precise, let us ask ourselves who is the God on the first mention of word "God" in John 1:1? Who is the God on the second mention of the word God in John 1:1?
If the God that the word was with is the only true God/ the Father, then we can say that the God that was first mentioned in John 1:1 is the Father. Do we have record from the Old Testament that the Father is the Creator God. Malachi 2:10, Mark 13:19; Matthew 19:4.
Let's now go to the second mention of the word God in John 1:1 the word was "God".
Note that both "God" in the same verse are capitalized, thus they are given the appearance that both Gods are the true Gods.
Examining the word was "God". Are there verses in the Bible other than John 1:1 that show the word was the almigthy God that the prophets spoke about and wrote about as their God YHWH?
I cannot find a verse that show the Almighty God's name is "Word" and worshipped as God. Nothing in the bible is written about the God named Word as the Creator.
When I asked this respondent who is the Deity twice mentioned in John 1:1 his reply in the comments section was;
"There is only One Deity. Only one divine nature. Only one divine substance can exist ('substance' meaning 'Spirit'). And it is revealed that that 'substance' is shared (in a perfect state of loving union) by Father and Son, in One Holy Spirit. But these things must be experienced - through God-given repentance and Spirit-wrought faith. Else they will not be known. This is the new birth, of water and of Spirit, a birth from above.
Such answer show sophistry, not precise language.
3 in 1 and only 1 divine nature, 1 of the 3 (Jesus) was split and has 2 natures. Where is the basis for this? Is the Deity in John 1:1 and the rest of the bible the "Father and Son, in One Holy Spirit"? Jesus is not even in the Old Testament. Granting that what was said was "precise" (which it is not) how is the 1/3 of God (Jesus) missing in the OT to be accounted for?