iPhone 7 audio problems - no audio devices found

I am unable to make or receive calls or use the voice recorder etc.

When starting the voice recorder app I get the error: "Recording Failed No audio devices found."

I have tried a hard reset and also a complete reset and restore from an iCloud backup. No change.

When I make a call, the call goes through but I am unable to hear anything (no ringing, no answer etc. but the receiving phone rings). I get the same results using just the handset or with a headset plugged in. I am able to make a call when using Bluetooth.

If I play music on the phone it plays through the internal speaker, but if I connect a headset the music is still played on the phone speaker.

It seems to be a problem with the internal audio.

I've read that this a a somewhat common problem for an iPhone 7.

I'm running iOS 12.2

Any advice will be greatly appreciated.