HELP

How to Recover a deleted email on your iPhone

1. Tap  in the upper-left corner, then tap an account’s Trash mailbox.
2. Tap the email you want to recover, then tap .
3. Tap Move Message, then choose another mailbox.

Here is the official Apple Support article on the topic.

Did you look in the trash/deleted items folder?

Then they are probably gone for good. Contact your email provider.