How do I download Safari for my iPhone 11?

Safari is installed on your iPhone 11 as part of the update of the iOS software on your phone. The Safari app is not one of the apps that can be deleted but with iOS 14 it can be removed from the home screen. If you have iOS 14, 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.

If that is not the cause, try using Search to see if that will locate it: https://support.apple.com/en-us/HT201285