microphone works at very low level

My new iPhone SE running IOS 16.6 seems to have an extremely low volume on microphone input. When I plug in an external mike the level is normal. For example using the voice memo the red waveform barely registers any amplitude, but with the external mike it spikes even with normal speech. Nobody can hear my voice when on a phone call (without the external mike). I've tried turning the phone on/off several times. I've tried several audio apps and nothing seems to work with the built in microphone. The mike does work, in the sense that a very weak signal is recorded, but it is so weak that nobody can hear me when I make a phone call.