But there is a difference of being in the "form of" and being "made in the likeness of".
Being in the "form of God" speaks to being equal to God.
My voice, my physical appearance is who I am - it is not a 'form' of me.
The "light" that was in the beginning was not only with God, but IS God.
I can respond to your post and say, 'You say'. I don't actually see you saying, 'But there is a difference ...' or hear you saying, 'But there is a difference ..' but I can see your post and see that you said, 'But there is a difference ... by your post. Similarly we can see what God said by his Word. The disciples could hear what God said and see what God was doing by seeing his Word doing it. His Word was in the form of light in the beginning and in the form of God when he appeared to Abraham.
What is the form of God who is invisible, who no one has ever seen or ever heard? Jesus said, "His voice you have never heard, his form you have never seen". In my understanding the form is 'He', in other words, the form of God would be the light that would reveal God and make him known. That's what John 1:18 says, "No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known."