IPhone 6s - Unable to hear callers unless on speakerphone

I am unable to hear callers when they ring my IPhone 6s, unless the speakerphone is switched on. However the callers can hear me at all times.

I've done all the tests shown online, but the problem still exists.

Clear/ clean the microphone socket.

Switch the device on and off repeatedly

Check volume settings

Unplug earphones ( never used anyway)

Squeeze front of device between microphone and camera

Switch off Bluetooth

Etc

Any other help would be appreciated.

Thanks