Chase the feeling! You said it yourself, you have a job to do. You'll have a job for a very large portion of your life, and you're going to have keep talking on the phone. But that's OK, cause you're a badass and you've proven to yourself that it's possible to talk on the phone (to a stranger, no less) without stuttering, so my advice is to keep on doing it. Good job, that shit can be scary. My rule is, if I screw up, then I don't dwell on it. That way I don't psyche myself out for when I inevitably have to do it again.