It's important to be prepared for your interview, whether it be a phone interview or face-to-face. Because the interview is one of the most crucial parts of your electrical engineer job search, it's best to be as prepared for it as possible before you even have it scheduled. The way to do this is to have your portfolio ready to go. It's always best to have a copy to leave with your interviewer or an electronic copy to send to them before the interview. It is always best to assume that they will need another copy for the interview; never assume that they have kept track of your original portfolio. Also, if you are working while looking for employment, this gives you a chance to give them the most updated version of your resume and portfolio.
Though both methods are very different, it is important to prepare just as much for a phone interview as for a face-to-face interview.