Thanks for reminding me of that (
also thanks to I think @Ruin who pointed it out first), but not FAS has been speculated and from what I have read about the divorce there were accusations from both sides about excessive drinking but FAS I don't think is a candidate in Phil's messed up physiology.
Personally, I think he just comes from two rather unfortunate gene lines combined with some weird physical issues that just never got treated when he was younger becoming more and more pronounced as he hurtles towards middle age and is piling on the pounds again.
For example I'm 95% certain that he has less movement in one of his legs compared to another we have a decent number of videos showing how he walks with the camera pointing at his feet his left leg does not swing out as far as his right ever and it seem's to point outwards a little less and he always seems to have that leg towards the back of the other in every full frontal picture we have of him and it's always ever so slightly bent so it's never fully extended, He also doesn't seem to like putting weight on that side of his body unsupported.
I don't think this is a conscious decision on his part I think it's one of those little things people do subconsciously to cope with some problems but when you notice one thing he's doing other things stand out as well and things start to make sense.