I want to become a sitter, but my account won't let me update past the phone number page. What do I do?

I want to become a sitter, but my account won't let me update past the phone number page. What do I do? Whenever I try to create my profile and I type in my phone number, it says "the phone number is already listed". I really want to become a Rover sitter, but I don't know what to do.