I would agree that an in-person interview would be better and would help you really get to know the program/city well too. Also, are you good at phone interviews? I personally am not too great at phone interviews but I can handle in-person interviews pretty well. In-person interviews allow you to use body language and appearance to show confidence (or not), whereas during phone interviews, it is all about the content of what you are saying. think about these factors (maybe thinking back to past interviews you have done) and you might realize that you perform better in a certain type of interview.
it seems, though, that taking the time to visit the school shows that you are very interested and committed to the school you are applying to, but then again, if you decide that you rock during phone interviews and bomb during in-person ones, it would be better to do the phone. I'm sure with preparation that you'll do great in either!
hope this gets you thinking!