How can I recover permanently deleted photos on iPhone?

The thing about the word permanent is it is well......PERMANENT, meaning a condition which cannot be reversed. If you backed up those photos somewhere, like another backup service (Amazon Photos - Google Photos, etc.) or to your computer, then sure you can go there and they would be safe. But if you permanently deleted photos, which were not backed up elsewhere, they are PERMANENTLY GONE.

Do you backup your iPhone to a desktop Mac or the iCloud (not iCloud Library)? If so you should be able to restore them from the backup.