Use Voice Isolation to Sound Better
Granted, this isn’t an accessibility feature per se, but you can still use it as one if you have some form of speech impediment.
As you can guess, this feature isolates your voice during phone or FaceTime calls so the other person doesn’t hear the background noise around you.
This feature works surprisingly well, and all you need to do to use it is to open your Control Center when you’re on a regular or FaceTime call. Then, tap Mic Mode and select Voice Isolation.