Grey out the Speaker while calling and unable to speak and listen during calls?

I see you are talking about an iPhone 7. What you describe is 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.

If you have a hearing or sound issue on your device then please try some of these processes to set it right

1. If you have a distorted sound issue on your iPhone --> If you hear no sound or distorted sound from your iPhone, iPad
2. If you are not able to hear the other person, click this...>If you can't hear a person on a call or voicemail or if the sound isn't ...
3. If you only hear through speakerphone mode --> If your iPhone is stuck in headphone mode - Apple Support
4. If the other person is not able to listen to you then please click this to identify the issue --> If the microphones on your iPhone, iPad, and iPod touch aren't ...

If the above options do not mitigate the issues then Contact your carrier and then Contact Apple Support