Prepare just like you would for a real interview. Brush up on some of the more common interview questions and have some responses prepared. Think about some clinical situations that you've encountered that you can use to highlight your strengths and answer questions like "describe a time you've had a conflict with a co-worker."
Dress professionally for the interview. If you dress professionally, you'll feel more professional and that will come across in your voice. Sit in a straight-backed chair- not on the couch or bed and don't walk around during the interview. Eliminate all background noise like TV, radio, road noise, etc. Smile when you speak on the phone. Use a land line for the call, if possible, or make sure that you have good cell phone
reception. Speak slowly and clearly, and loud enough to be easily heard without shouting. It's harder to understand conversations on the telephone, and you want to make sure you are understood.
Have a list of questions in front of you that you want to ask. Also have your resume in front of you so you can refer to your qualifications. Good luck.