App store has disappeared

go to settings-general-reset-reset home screen it wont look like it did anything but it does check again if its still not there check your utilities folder or another folder on your phone

It's a pre-installed app and therefore cannot be deleted so you may have inadvertently moved it onto a screen or into a folder. Check all screens and folders and do a search in Spotlight, it will tell you if the app it still on your iPhone but unfortunately not where it is. If you find it on one or your screens or in a folder, press the icon until it wiggles and then drag it back to where you want it. Alternatively you can reset your home screen in Settings>General>Reset>Reset Home Screen Layout.