Restoring lost phone icon on iPhone

Are you referring to not seeing the Phone icon on your Home Screen? If that is the case, then swipe all the way to the left until the App Library appears. Find the Phone icon, then press and hold and drag it back to the home screen.

Swipe all the way past the last window on the home screen until the App Library appears. Search for "Phone" on the search bar and drag it back to the home screen. Your phone app should return to your home screen.

You're welcome.