Terrible Mic Issues with brand new iMac

Hi -

I seem to be having a terrible sound quality issue with my new iMac's mic. It seems to only be an issue when communicating with someone else's iPhone while I am on my Mac, ie, when they use FaceTime with me, or basic phone calls, or when they use zoom on the phone. It's not an issue otherwise. Is anyone else having this problem? I've looked at other threads, and there's no advice or help given-- just someone coming on to tell people with this problem to contact support. Any advice would be most appreciated, please. Thanks.