how to recover permanently deleted photos on iPhone

Permanently deleted does exactly what it says when you delete photos from the Recently Deleted folder or if it has been longer than 30 days. You would need to have a backup of those photos in order to recover them. You can view your last iCloud Backup by going to Settings > [name on top] > iCloud > iCloud Backup, to see if the last backup was before the time you deleted them. Your photos are only stored in the iCloud Backup if you are not using iCloud Photos.