Just so you know, it is the icon that looks like a blue letter that you are looking for and typically it should be in the dock at the the bottom of your iPhone Home Screen. Having said that, you may have deleted it or moved it into a folder by mistake.
First do a search for it. Pull down from the middle of any Home Screen to invoke the spotlight search. Type Mail into the text died at the top. If the app icon appears in the search, and if it is hidden in a folder, the name of the folder will appear to the right of the icon.
If that fails, and you did delete it, you can download it again in the App Store.
Restore a built-in app that you deleted
- On your iOS or iPadOS device, go to the App Store.
- Search for the app. Make sure that you use the exact name of the app. Find the correct name of built-in apps.
- Tap to restore the app.
The correct name of the app is Mail.