I think most Christians would say Phelps is just a nut. It isn't like he has a big following. We only know of him because of his extremism. He drags his family along with him but usually there are only a very few people with him. He's certainly not an example of mainstream Christianity.
Not to mention that there are significant indications that Phelps is a paid shill for the leftists. His "church," which consists of himself and his family members, is mighty cozy with Democrats.