I've had a mild stutter since childhood-My last several jobs all involved significant phone time. I have found that once I get in the rhythm and become comfortable with it, it becomes second nature. The first few calls might not be ideal, but say your new if you freeze and noone will care. Also, try to tackle the weirdness of talking on the phone with someone observing you. I hate it, but I get used to it. Practice is key. You will be fine.