The content of a telephone interview will be very much like an ordinary face-to-face interview. The questions will be the same: the interviewer will be trying to find out about your qualifications, your experience and your reasons for wanting to work for that school / in that country.
Given that the interviewer will not be able to see you, (s)he will be paying a lot more attention to your voice. It's a good idea to sit up straight and to hold your chin up. This will help you sound more confident and professional. Sales people recommend smiling while you are speaking on the phone; they say it helps the voice sound better.
You could always do a trial run with a friend on the phone and ask him/her to give you feedback on how you sound. If you don't want to do a full interview at least have a conversation and ask for feedback on how your voice comes across.