It is not be possible to delete the App Store app; the worst you could do is to remove it from the Home Screen and it should still reside in the App Library - which follows the Home screens when you swipe across. It will also be in a spotlight search result initiated by swiping down from the centre of the screen.
In the Library it can be found in the group called Utilities. If you touch on the smaller group of icons the whole folder should open to reveal all the apps within. App Store will be visible there. Touch and hold, then drag it to a Home Screen.
The only time you won't see App Store is if your iPhone is managed by a parent or with Mobile Device Management in a school or work environment and the manager has hidden it from view to prevent unauthorised use.