Can you flip the script? If you're already ok with quitting and it's not a financial issue for you, this is a unique opportunity where you get to practice speech with many different people that you'll never hear from again. Could you use it as an opportunity to try things out with your speech? Like, what would happen if committed to not rushing yourself, even if they get angry or hang up. Or practiced taking a calm breath instead of trying to et out "hello" as quickly as possible. Worst case scenario if you'll be fired, but you may already be expecting that so whatever. I say play around with it and use the opportunity to explore your speech and try some counter intuitive things.