This article explains how to add, delete, and create Smart Folders in the Inboxes screen of the iOS Mail app, so you can focus on unread email, VIPs, attachments, and more. Information applies to iPhone, iPad, and iPod touch devices running iOS 12, iOS 11, or later.
How to Add Folders to iPhone Mail | How to Manage Email Messages on Your iPhone
The Mail app comes with a selection of smart folders that you can turn on or off, as well as an option to add custom smart folders. To enable smart folders that focus on specific types of messages in the Mail app:
Open the Mail app and go to the Inboxes screen.
Tap Edit at the top of the screen.