According to your case, it's a pity you can't.
The Recently Deleted folder is the last chance to recover the deleted photos after deleting them on the iPhone. Moreover, you don't have iCloud or other backups.
Next time, be so careful of clearing the deleted ones in the Recently Deleted folder. Or you'd better make a habit of doing backups.
You can also ask the Apple assistant for some help.
Also read: Recovering Deleted Photos on Android and iPhone