Someone who's more familiar with lifting weights can give you a run down of why he has the body type of a man who's never bench pressed or lifted a set of dumbbells before in his life. But you don't need to be an expert to debunk that people used to stop and stare at him and say "Holy shit dude, Phil's ripped!"
It's not just his appearance, it's what goes into maintaining that kind of physique - we're talking about borderline autistic commitment to diet and exercise regimen. Contrast that with the Phil we know and laugh at who thinks lifting a gallon of milk without arm strain is a feat of strength. There's also no photos of it which is bizarre for somebody who's basically lived online for the last twenty-odd years and even uploaded really cringey pics like that "Punisher" cosplay on his old "Top Haters" site.
Phil was always a plump pig from what I understand, the dudes arms (triceps) are completely without form and lack any form of mass below his shoulders, it's just nothing but fat and skin.
He wasn't always a plump pig. I can't find it but there's an old photo from + or - the early 2000s where he is legit skinny and looks like a wannabe Columbine shooter. Remember, he was 17 when those shootings happened and was a HUGE edgelord in his early Internet days. My guess is that he turned into the Philsbury Doughboy during university - we don't know much about his parents' cooking beyond the infamous Authentic Italian Sauce but we do know that he will live on huge amounts of junk food when left to his own devices. The only real question is whether that happened as soon as he moved away or only after he stopped living on campus.