Screen mirroring on an iphone 7plus

Hello and welcome to Apple Support Communities, chrisfrometobicoke.

If I understand your post correctly, your iPhone is not responding after you tried to start screen mirroring. I’d like to help.

Follow the steps in this article:

Restart your iPhone

Then follow the steps found here:

If AirPlay or screen mirroring isn’t working on your device

Let us know if that resolves this issue for you. 

Thanks for using the Apple Support Communities. Take care.

Hello chrisfrometobicoke.

In order to isolate and fix this issue, you will need to restore your iPhone. Before you attempt any restore, I recommend you save and back up your iPhone’s data. Steps on how to back up an iPhone can be found here: How to back up your iPhone, iPad, and iPod touch

Once the backup has been completed, you can restore your iPhone. Steps on how to restore an iPhone can be found here:  Restore your iPhone, iPad, or iPod to factory settings

Once that's done, I'd recommend setting your iPhone up as new, and testing it out before restoring from a backup. Check out this article for those steps: Restore your iPhone, iPad, or iPod touch from a backup

Cheers.