Restoring permanently deleted emails on an iPhone might be challenging, but here is how you try: Start by looking in the Trash or Deleted Items folder on the Mail app. If they are still in there, simply drag them back to the folder where they came from.
If the emails have really vanished, you will need to use backups or data recovery methods. If you have a recent iCloud backup, you can restore your phone to that date and hopefully recover the emails.
Otherwise, you may have to use specialized data recovery software, but there are no guarantees of success.
