Prepare for a phone interview the same way you would for an in-person one; research the company and have a few questions ready for the interviewer. This is likely a pre-screen, so I wouldn't imagine there would be too many behavior-based questions, but you might as well prepare some of those as well (e.g. "tell me about a time you had to resolve a conflict...").
Some people recommend getting dressed the way you would for an interview--the clothes help you put on a more professional tone on the phone. I have never gone this far, but I do make sure I'm in a quiet setting, with note paper available, etc.