Phil's been a pro for TEN YEARS now. Well, 9 and a half. He's been on Jay's super secret stack for a lot of that time - remember he crashed with Jay for a bit, learned the ropes, and voila, became a top pro overnight.
And he didn't have 15 years of natural "base" bodybuilding training, like you see with a kai or a ronnie. They took their natural ceiling to the max, THEN got on the pro stack. Phil went from 1st show to winning pro card in what, 18 months?
So yeah, at some point, his arms, shoulders, calves will peak, and his midsection will begin to expand. it's not a knock on phil, it's just science.