Danny Eberhardt,
Just to clarify, when playing back the recorded memo in Voice Memos, everything sounded fine, is that right? Also, when testing via FaceTime audio call (instead of a standard call), was the other person able to hear you fine? If it did sound fine on the FaceTime audio call, this can indicate an issue with the carrier's network, and you may wish to try reaching out to them for further investigation.
If it also happens on FaceTime audio calls, we'd recommend reaching out to Apple Support for further investigation: Get Support
Be sure to also check for any updates available, such as the newer iOS 15.0.1 update: Update your iPhone, iPad, or iPod touch
Also, try restarting the iPhone, as this can help with that type of issue: Restart your iPhone
Cheers.