I was working in retail and then ended up in a call centre so I was doing the same thing over and over, saying the same things over and over. I guess I didn’t stutter because saying ‘is that all for you?’ or ‘do you want a receipt with that?’ started to become a habit. My advice would be to find a routine. If you need to call people at work then make up a script and recite it every time you’re on the phone.