I've had a few in the last couple of weeks with a potential employer, I can't speak for all companies of course but it was very relaxed and just questions about what I do now, how I do them, what systems I have experience with etc. I haven't yet been asked one of those tricky questions that really make you sweat.
The advantage of phone interviews is that you can write very brief notes and bullet points that you think may be useful on a couple sheets of paper in front of you, but don't touch them, they don't want to hear you flipping or rustling sheets of paper. If you do get a bit stuck for an answer if you've got something prepared then you'll be more relaxed and come back with well thought out answer rather than going "uh....uh...."
Do some research on the company you're applying to, better still the department or position and make a few bullet points about what they do etc.
Have small list of your strengths and weaknesses.
Have an example of a situation where you overcame a problem.
Have an example of a project you have seen through to completion.
Put down some career aspirations, where you'd like to be in 2, 5, 10 years.
Why you are looking to change jobs.
Why you want to join this company.
Why you would be good for this position.
....and lots more, google common interview questions or something.
Common sense things really and the things that commonly come up in interviews, but do keep the points very brief just as a trigger for your memory, you don't want sound like you're reading something.
Also try to answer questions without waffling on too much and ending up completely off topic - I'm guilty of this
Good luck