iPhone 7 Plus mic not working for siri

Perhaps this article willl help:

If the microphones on your iPhone, iPad, and iPod touch aren't working - Apple Support

where it says: If Siri can't hear you, make sure that the receiver and front microphone on top of your iPhone aren't covered or dirty.

Just in case if you want to try to restore it, here are the instructions for that:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

And here you can find the nearest Apple Authorized Service Provider.

Or head here for Genius Bar Reservation and Apple Support Options - Apple

iPhone has different mics responsible for different things.

The one that works for Siri and front-facing videos is placed under the speaker grill. So it sounds like that it’s broken, cause you said that hear your voice on a recorded video.

One thing to try before going to the Authorized Service Provider is to restore your iPhone to factory settings and set up as new and test.

But I bet it will be a waste of time, so if I were you, I’d show up at a Genius Bar or the nearest AASP.

Can you record a front-facing video and report if the sound quality is crystal clear?