The Mayo phone interview, geez, I forgot that one!
I wouldn't worry. Its a little awkward, I mean, sitting in your apartment answering these questions, but I actually didn't get stressed at all. I mean, its so laid back when you don't have to put on your suit and make travel arrangements, etc (of course, if/when you get an on-site interview, then you will, but I am trying to say its way less stressful than regular interviews).
My only complaint about the phone interview is that the questions are worded very, err, negatively? The word choice can be very one-sided. Like one question was "Would you ever give up on a patient?". Ok, yes, at some point you realize that every patient will not survive, but that doesn't mean you just toss your chart to the side and never see them again. The questions leave you in awkward situations, and since you aren't there and your answers are transcribed, its sometimes hard to find an articulate yet heartfelt response. But everyone goes through it, and I wouldn't suggest preparing answers--its better if you just are natural, cuz they can tell when you sound rehearsed!
Just my 2 cents, hope it helps and good luck!