How can I recover photos deleted after turning on Icloud photos? They aren’t in my icloud

The usual reason for photos being deleted when iCloud Photos is turned on is that the photos were originally placed onto the iPhone by syncing them from a computer (using iTunes or Finder). In that case, the photos should still be on the computer and can be manually uploaded from the computer to the Photos app at iCloud.com and they will then sync to the phone. Another option is to AirDrop the photos to the phone. See that and other information in the "What if some of my photos and videos are missing after I turn on iCloud Photos?" section of Get help with iCloud Photos - Apple Support