Microphone

please click this to identify the issue --> If the microphones on your iPhone, iPad, and iPod touch aren't ...

Cellular Phone calls and invoking Siri (hold home button or side button) use two different Microphones on iPhone.

Test both Apps, which app has a Mic issue should identify which Mic isn't functioning.

You can probably call Apple Support and ask them to run remote diagnostics to 100% confirm a Microphone hardware isnt detected or has failed rather than it being a software iOS issue of some kind.