Google Pixel 7a microphone is quiet, muffled or not working

The checks in more detail

On the Pixel 7a the main microphone is on the bottom edge, with another near the top, so a case that covers the bottom edge or a plug of dust and lint muffles it. Remove the case and clean with a soft dry brush. Next check Bluetooth, because a connected headset or car takes your voice even when you are holding the phone, so turn Bluetooth off, and unplug any USB-C headset or adapter. Google's page for people who cannot be heard lists the same checks and adds restarting the phone and testing in Safe mode, which turns off third-party apps.

If the fault disappears in Safe mode, a call recorder, a noise app or a voice changer is probably intercepting the microphone, and removing recent apps cures it. Check app permissions in Settings, Apps, the app, Permissions, Microphone, since a denied permission gives silence in just one app, and in Settings, Privacy, check that the microphone access toggle is on, as the Pixel 7a has a quick switch that disables microphone access for all apps. Try the call on speakerphone and with the handset to see whether one mode fails, which points to a particular microphone. Install pending updates.

A phone that lost its sound after being wet may need to dry, and one that fails every test needs service. Back up, then ask Google or a repairer. If the problem appears only when recording video with the rear camera, remember that the Pixel 7a uses different microphones for different camera modes, and a covered rear microphone beside the camera bar gives a muffled video while calls are fine. Clean that area as well, check the camera app's audio settings for any option that focuses sound, and test in the video mode you actually use, since a fault confined to one mode points to one microphone and tells the repairer where to look.