I don't think Phil has a degenerative condition other than "getting older, never exercising, and drinking too much gin". He was always soft, kinda fat, weird build, bitch tits. Then over the past few years, he lost some weight, but what weight he lost was the little bit of muscle he had. Now it's just the fat left, jiggling around while he wobbles on bird legs, and has the same weird proportions.
The lesson for you kids is, get more exercise than just picking up a game controller or buying groceries.