Unless you're Skyping instead of talking on the phone, she has no clue what you look like or what you're doing on the other end of the line. It doesn't matter if you're sweating bullets, pacing every square inch of your room, or squeezing the life out of a stress ball. You could be wearing your rattiest sweatpants, the ones that are a single wash cycle away from falling apart, and it doesn't matter. She won't know. In fact, there's an excellent chance that she'll be nervous, too. Just try to keep your voice relaxed and friendly, and take out your jitters elsewhere.