Accidently deleted the "Photos" app icon on iphone. How do I get this back?

Use App Library to search the app you are looking for, see -> Organize the Home Screen and App Library on your iPhone -> Organize the Home Screen and App Library on your iPhone - Apple Support           

• If you have find the app, tap & hold on the app, then drag to the Home screen & drop it.

If you didn't delete the app and only deleted the icon, it is likely that the icon is still in your app gallery.

Find it in there and then drag it back to your home screen of choice.

I'll be back with a link to show you how (watch for an edit to my post).

Edit: Raicya has posted the link