None. As a fully wizarding household they do not use muggle telephones.
Creator of question: But in the 4th book, Ron and Mr Weasley try to call the dursley's on a telephone. What I mean is, has J.K Rowling said in an interview their number in the 4th book.
There is no indication that the phone Mr. Weasley used was a phone in their home. The fact that Mr. Weasley was unaware of the most basic elements of phone etiquette should amply demonstrate that he was completely unfamiliar with telephone usage, ergo, there is no phone in their house, ergo, no phone number to list. Sings-With-Spirits 15:13, June 22, 2011 (UTC)