How to install safari browser on iPhone 12 pro

I understand you are unable to find the Safari app on your iPhone. To find it, please read Find your apps in App Library on iPhone - Apple Support. To move it your iPhone's Home Screen, refer to Move an app from App Library to the Home Screen.

You cannot download Safari as it cannot be deleted from your phone. The only thing you can do is remove it from one of your Home Screens. It will always be available in your App Library and you can find it there by swiping all the way to the left on your phone. The App Library is one page past your last Home Screen.