People couldn’t hear me when I called from a Nexus 5x phone, after a security update for Android 8.1.0 early October 2018.
This was fixed by wiping the System Cache Partition. This will not delete your files, but it’s best to backup everything.
- Switch off the device
- Press & hold the Volume Down button and press & hold the Power button simultaneously until the phone turns on. You’ll see the word Start with an arrow around it.
- Press the Volume Down Button twice to highlight Recovery mode.
- Press the Power button to start Recovery mode. An android robot will show up with a red exclamation mark sign.
- While holding the Power button, short press and release the Volume Up button, a menu will show up. (do NOT hold the volume Up button as this will reboot your device!).
- Use the Volume buttons to scroll to Wipe cache partition and press the Power button to select it.
- After this, select Reboot device from the menu with the Power Button.
That fixed it for me.