How do I restore the Safari icon to my iPhone screen?

The Safari app is not one of the apps that can be deleted but it can be removed from the home screen. Go to the App Library (swipe left past your last home screen). From there you can touch and hold an app and slide it left back to the home screen.

Another reason for it not being visible is due to a restriction. Go to Settings and tap Screen Time, tap Content & Privacy Restrictions, tap Allowed Apps. See: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

Swipe all the way to the right until you get to the App Library. press on the Safari icon until it wiggles, then drag back to your home screen.