#You can use Spotlight Search find and restore the missing calculator app icon simply by searching for it. From there, you can launch the App and use it or add it to your Home screen.
1. Be on your iPhone Home Screen (default) and swipe down from the middle to
open Spotlight Search.
2. Type Calculator.
3. From the search results, tap the calculator app icon to open it.
4. Else, press the calculator app icon and drag it down onto the Home Screen to add it
there.
#Additionally, you can also find calculator in App Library, which you can access by swiping left on the very last Home Screen page.
You should find the App Store in the Utilities folder of the App Library. Just like above, you can press the app icon and drag it left to add that app to the Home Screen.