You dictionary is probably just out of date. While I agree with your dictionary that hippoppotomonstrosesquipedaliophoia is wrong, so is hippopotomonstrosesquipedaliophobia. It could also be that the person who wrote the word on the dictionary wanted to shorten it by a lot because he has hippopotomonstrosesquippedaliophobia. I can't believe that he shortened it so much though. I hope the poor guy conquered his fear.