Prepare yourself as you would for any interview. Some people may be able to pull off doing the phone interview in their pajamas, lounging on the couch, but I find dressing the part and sitting at a table or
desk mentally prepares me much more. If possible, I recommend using a landline where you are less likely to have a dropped
call, nor will you have an issue with clarity of your voice. As the article said, your voice is your only tool in this interview, so I would probably have a glass of water nearby so that you can ensure that your voice is in its best shape (you don't want to go hoarse in the middle). Keep a pencil and paper ready so that you can take notes on what the offer is and if you need reminders about the question or write down your own questions to ask later. For that matter, try to think of questions that you might have about the position and its requirements before the interview so that if they are not answered, you have them available to ask at the end of the interview.
Keep your answers brief and concise. It's pretty easy to ramble on when you don't have facial expressions to judge whether or not the interviewer(s) understand your answer. If they need clarification, they should ask for it, if you feel that you haven't answered the question in a manner that they might understand, you can ask if you sufficiently answered it.
Don't use slang unless it is pertinent to the question and relevant to the field. Good luck and let us know how it goes.