Make sure your iPhone and Mac are signed in with the same Apple ID
Turn on Wi-Fi and Bluetooth on both devices
On your Mac, open Control Center
Click Screen Mirroring
Select your iPhone from the list
On your iPhone, tap Allow if prompted
Enter the AirPlay code on your iPhone if shown
To stop mirroring, open Control Center on your Mac and click Screen Mirroring again
If Screen Mirroring does not appear, check that both devices support AirPlay and are on the same network