What can we talk about on the phone?

You also might try either shortening the conversation (end it early) and/or not talking everyday - I know from past relationships that things can get a little stale, and that might help. The only thing about that is you have to make it absolutely clear that it's not because you don't like him - you do, but would just rather not have the awkward silences.

I would suggest some kind of joke. Or something light to break the silence. I think it really depends on the direction of the conversation. You can always ask questions. Guys love to talk about themselves!