My advice would be to not worry about stuttering. Basically impossible, I know, but you are going to stutter. Its a fact. But, so what? Focus on stuttering easily and with as much control over it as you can. Answering the phone is where you block? Reduce your rate and easy onset that shit! Didn't kill it this time? Someone else will call soon, so you will get another try. Every time the phone rings is another chance to do a good job. Working with the public gives you lots of chances every day to succeed. I'd wish you good luck, but you don't need it. 'Cause you got this.