Accidentally deleted Find My Phone from my new iPhone Xs

You can’t delete it. It is on your phone somewhere.

You may may have accidentally hidden it in a folder. Swipe from screen to screen to look for it. Do a Spotlight Search. Swipe down from the middle of a home screen and type Find my iPhone in the search field. When it shows up, you will see the folder it is in (if it’s in a folder ) next to the App Name.

You can also Reset the home screen layout in Settings>General>Reset>Reset Home screen layout and that will return the app to the home screen. It will also return the home screen to out of the box condition ruining any folder structure you had on the home screen.