After the ios 15.7.3 update the mic of my iphone 7 plus stopped working

Yep. These are all signs of an  AudioIC hardware issue. You can:

1. Do an out-of-warranty replacement of your iPhone.
2. Trade in your iPhone towards a new one.
3. Find a competent 3rd party repair site that can do the soldering repairs need, but no guarantees. Also, if you go this route Apple may refuse service on your iPhone in the future.

Hello euqufu,

For difficulties with your microphone, you'll want to take the steps below:

Clear the microphones

1. Remove any screen protectors, films, or cases from your iPhone.

2. Clear any debris from the openings of your iPhone. 

If people can't hear you on phone or FaceTime calls

1. Open the Voice Memos app. 

2. Tap the Record button , speak at the bottom of your phone, then stop the recording. 

3. When you play back the memo, you should hear your voice clearly.

If people can't hear you when you're using speakerphone 

1. Open the Camera app.

2. Record a video while speaking at the top of your iPhone.

3. Tap the camera chooser  to switch to the other camera. Then record another video while speaking at the top of your iPhone.

4. When you play back the videos, you should hear your voice clearly.

You can also find those steps in this resource: If the microphones on your iPhone aren't working - Apple Support

Should that still continue, you'll want to reach out to Apple Support: Contact - Official Apple Support They'll be in the best position to look into your options further.

Take care.

Same. The microphone icon is greyed out when trying to make a call. When trying to use Siri, Siri closes instantly. I cannot hear anything when calling or receiving a call on the phone, but I can make calls with my paired Apple Watch 6.

iPhone 7 Plus 128GB Jet Black Universal - Originally activated on a Verizon MVNO, currently on Xfinity Mobile

iOS 15.7.3

I did the hard reset by holding volume down and the wake/sleep button, to no avail. I called Apple Support. They ran diagnostics, nothing came back wrong. They had me "Reset All Settings," that didn't work. They told me that I'd have to take it to either the Apple Store, or an Apple Authorized Service Provider. I asked for a CS code, and was denied. I don't have money to shell out for a replacement or a new iPhone.

Same here…

I think the factory reset and than instal an old version of iOS should help. or maybe a new version of iOS probably

This exact thing is happening to me too. Same problem, same symptoms. Dead air on calls both ways, mic is greyed out on video recordings, SIRI pops up for a split second then closes, memos recording button doesn’t work, etc. I did a factory reset and it started working again, but then it stopped again less than 24hrs later.