If you have been given a CHOICE between a phone interview and an on-site interview, I believe it is always better to opt for the interview at the medical school.
The phone interview has only one thing going for it: it saves money and time. Not insignificant items, to be sure, but unless you are really financially strapped, there are times in life when spending more is a good investment. You have already invested a considerable sum (money; time; blood, sweat and tears) in your undergraduate education), you will invest even more of these during your medical education, so why skimp now when you may have an better opportunity to choose where you get that education?
In a phone interview you have no way of
assessing how the interview is progressing. There are no body language clues, no eye contact. Nothing but disembodied voices at both ends of the line. Not satisfactory at
all.
Another important reason to have an interview at the medical school is that you have a chance to interview the medical school, so to speak. You should be speaking with medical students about their experiences at that medical school, costs, housing, quality of education, quality of life, safety issues, even when and where to have fun. Are they relaxed or uptight? Ask students about the clinical experience. If you can before the interview itself, ask about what the interview is like: questions asked, more than one interviewer? common questions? whatever else you are worrying about. Be sure to go on the tour of the school if that is offered; if not offered, ask some medical student if he/she is willing to give you a quick tour.
If you take the telephone interview, you have no opportunity to do any of the above.
If you get admitted, and have other acceptances, how do you choose where you will spend the important next four years of your life? The most "prestigious" school, the least expensive school, the one closest to home? How will you know what is the best match for YOU, where you will thrive best.
Thriving is an important component in both learning and earning high grades. In this particular instance, you will likely turn down a Mayo acceptance because you know nothing about the school, when in fact it might have been the best match for you.
Whatever your choice, may the Force be with you.