Effective and polite way to end a phone conversation
When talking with friends I generally end with one of the following.

好，就这样吧 = That's it (kind of, hard to translate)
好，我走了啊 = I'm off now
好，下次再聊 = Talk again soon

Or of course, the very simple 好，拜拜！
Looking at that, I guess I like to say 好 a lot!
Hope that helps.