How do I restore the App Store on my iPhone?

Unless you live in the European Union, it is not possible to completely delete the App Store from your iPhone. You might have removed the icon from your Home Screens, though. In that case, you would need to run the App Store from your App Library, or restore the icon to a Home Screen from the App Library.

Find and use your apps in App Library on iPhone - Apple Support

If you are in the European Union, you could have gone to special trouble to delete the App Store altogether (in favor of an alternative app marketplace). In this case, the App Store would not be in the App Library, and you would need to follow the directions in this Support article to reinstall it.

Delete certain built-in apps from your iPhone or iPad in the European Union - Apple Support

You can also search for it on the Home Screen.

Use Spotlight Search on your iPhone, iPad, or iPod touch - Apple Support