When the microphone isn't working in other apps, how are you conducting those communications? Are they video calls? On speakerphone? It could be they are using a different microphone than when you're making a proper phone call.
If that's the case, first thing I would do is just clean the debris out of any microphone grills. Most smartphones have at least three microphones. One on the bottom edge of the device for phone calls, one on the back near the rear camera for video calls and one near the top edge of the phone for front facing camera operations. Speaker phone and video calls would likely use that microphone rather than the bottom mic like a traditional phone call would.