Hello Wellsy68AFC,
The article you came from, If the microphones on your iPhone aren't working - Apple Support, is a great resource for testing the microphones on your iPhone.
There are multiple microphones on your iPhone. From what you are describing, it appears that one of those microphones is not working as it should.
Go ahead and perform a force restart. These steps can also be found at Force restart iPhone - Apple Support:
1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the side button.
If the issue continues after this restart, then we would suggest having the iPhone examined by an Apple Authorized Service Provider.
Information on iPhone service and available options can be found here: iPhone Repair & Service - Apple Support
Have a good day.