I always talk before I answer the phone and then answer it with the lead off of my previous speech being what I will introduce on the phone and I say it in a rhythmic fashion so I can't stutter. (It's sounds weird but it usually works and puts the other person at ease for when I will inevitably stutter because the initial line was well delivered). mentally , I have a phone accent / persona, and it helps me to feel more calm. Something like : "Ooookaaaay , let's Answwer the phooneeee *answers*, hello-this-is-(nameeee)-speaking-from-(companyyyy), howww-can-i-hellp-youu?"