Sadly, as much as we would all love Harry Potter star, Tom Felton's phone number, it is not available to the general public. The only people that have access to his number would be his friends and family, or people that he chooses to give it to.
However there are other ways to get in contact with the actor, if this is what you want to do... there are ways write to him, or you could even request his autograph!
Here's the address you need:
ID Public Relations
Pall Mall Deposit
124-128 Barlby Road
London W10 6BL
This is Tom's fan mail address, so you can send letters or requests for photos or autographs, and they have the best chance of getting to him. If you want an autograph, you also need to send an addressed and stamped envelope along with a picture of yourself so that it can be signed.
In my opinion though, the best way to get in contact with celebrities these days is to use social media. Tom is on both Facebook and twitter.
He can be contacted using either of these sites, although I've noticed he's more likely to reply to fans on Twitter.
Tom has a lot of people trying to contact him everyday though, so he may not always reply to your communications. But be sweet and persistent, and you should get his attention eventually.