This article describes the difference between archiving and deleting a Gmail message and how to enable or disable this feature on iPhone, iPad, and iPod touch.
Mail archives Gmail messages rather than deleting them:
When you archive a message, it moves to the All Mail folder. It does not delete the message from the Gmail account. You can learn more about the Gmail archive feature in Gmail Help. Archive replaces all delete options when you use a Gmail account, including tapping the Trash icon while you view a message and selecting Edit to manage multiple messages.
You can disable this feature in Settings > Mail, Contacts, Calendars > Gmail Account > Account >Advanced > Move Discarded Messages Into:
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