How do I re-download the App Store on my iPhone?

The only region where it is even possible to delete the App Store is in the EU. For most users, you will not not see it on the screen for one of two reasons:

• It it is the App Library and you can find it by swiping all the way to the left. By swiping down on that screen apps will be arranged in alphabetical order, so if it is there you will find it towards the top of the list and can return it to a Home Screen.
• You have Screen Time restrictions placed on your device that prevent using the App Store. This can be done by an Organizer if you are using Family Sharing. It can also be placed on an individual device and the location for that is Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases, Installing Apps. This needs to be set to Allow. You will not be able to access it if someone has set a Screen Time Passcode on your device.