Speakerphone not working but close mic and voice recorder work

Hi all,

A few days ago the speakerphone function on my S5 stopped working. The close mic (earpiece, holding phone to the ear) still works fine. Testing using voice recorder shows that BOTH mics still pick up sound fine (in interview mode), the top mic less so but still of a noticeable volume. Video recording with sound using the camera app still works fine.

In fact, the "speakerphone" mic is only broken during calls from the native phone app and using Skype, Facebook Messenger, Whatsapp (both with and without video, though the close mic still works).

The opposite party can still hear if I "flick" the phone, there's a clicking noise, but no audible voice (despite me speaking loudly). Confirmed using the Skype echo.

So I can record a video of myself speaking fine, presumably using the same microphone and camera as the messaging apps, then have no/very low volume when making a video call. The same apps will record my voice fine using the voice recording component of the app. It's just during the audio or video calls when it breaks down.

Tried reboot, safe mode, clearing cache, turning off/on noise cancellation, changing app permissions (within reason), and a few other things I forgot.

Many thanks in advance to anyone who can help!