Issue with Calls (Audio-In) on iPhone 5

iPhone 5 running iOS 7.12

Callers on the other end cannot hear me. Both outgoing and incoming calls from/to cell and landlines.

Have tried normal handset, speaker phone, Apple earbuds, third-party BT headset, all with no luck. Phone is not on mute

Any thoughts or suggestions? Seems software related, but I'm not very tech-savvy.

Yes - no issue with playback of recorded sound via voice memo app.