Siri microphone

It seems that my top front facing microphone is not working. I cannot get Siri to hear me, and there are a few other applications that don’t work unless I change the “listening” microphone to any other than the front top. Can I change which microphone Siri listens from?

I have cycled through all the obvious settings, reset my phone, updated software, reset network settings. Siri works fine when using apple headphones with the microphone on the volume control.

Thanks for any help.