I know I'm a little late but I got my current job from doing 2 of these. One with my manager and one with his boss. Let me tell you right now, I was VERY stressed out during the first one. It was my first time doing one of them. And what happened? It turned out to be a mellow experience. The phone interview is not JUST for them to interview you, but for you to interview them as well. Ask questions, seriously. You know, what's the day-to-day like, how is the work environment, etc. I am a pretty anxious person but I know just doing some deep breathing and getting a good night's rest before was a huge factor in keeping me cool. I had sticky notes of things they may ask including my answers just in case I blanked. Remember to smile. It may be over the phone but people can tell. And the person on the other end is a regular guy/gal. Don't sweat it. You got this, friend.