Hey man, I know how you feel. I work in customer service myself, so a big part of my job is talking on the phone. It is hard. Most of the customers I talk to are polite, but there are a few really shitty people I’ve come across. Honestly when people mock my stutter over the phone (which is VERY rare) I just try to tell myself that it says more about them and that they are probably just miserable anyway. It’s definitely hard to not want to clap back at them when it does happen, but it’s honestly best to just see them as what they are, losers. Don’t sweat it too much bro, you’re a champion for just holding down that job anyway