Yeah, phobias aren't a laughing matter at all. Take it from someone with a lot of phobias related to loud noises which have massively interfered with my life.
But I suppose if you don't HAVE to draw feet, there really shouldn't be any pressure to push yourself into doing it. Getting good at drawing shoes is probably a better skill to build for now, then you can take all the time you need in slowly desensitising yourself to feet. Your phobia may simply go away with time (as happened with me) or you might find a cognitive treatment that really helps. If neither is the case, then it's really not a big issue since most people wear shoes most of the time and no-one is going to notice if you hide feet using other objects.