Recover photos from iPhone memory
You would want to power off the phone immediately and then get a quote from a forensic / data recovery company if the data is worth paying for. I’m not aware of any tools to do recovery yourself, but perhaps someone else has that answer or an explanation why that’s not viable or cost effective. 

There are going to be all sorts of scam software, so here are two reputable companies that do recovery. One says they work with iOS, the other does not but I trust them for Mac recovery and they might have some recommendations worth exploring. 


https://www.ontrack.com/services/data-recovery/mobile/
https://www.prosofteng.com/data-recovery-services/


Since iCloud has a deleted photos album, be sure o check that as it works even without an iCloud backup. Sorry you’re in this place, too late to make a backup when the data is already gone. Try not to lose the lesson now...