Ive seen some people say his legs are prosthetic, but to me they look bulky enough to just be armour. The art style and stylized figures make it hard to determine sometimes.

Pharah is like that too. Personally, I think its just an ironman suit. Her limbs are on the skinny side, but I dont think they're prosthetic, I think that's just the figure they gave her. Her hands look more like gloves than when compared to Symetra's robo arm.

Having her be like this picture would be pretty neat though.