Memory is full warning
Ya know how in MS Outlook you have to Empty your deleted e-mails folder?... Well it seems "Photos" has taken the same process.
You can trash all the photos you want to make room on your iPhone. But those photos are not removed from your device so it really does not make more room on your phone!
To actually get rid of them (after you "trash" them you can go to Photos/Albums/Recently Deleted and you will notice a message that says they will be deleted in 30 days (or however many days are left until the 30 days are up). You can use the button on the bottom left to "Remove" the photos.
Apple says this is the issue now because people delete photos that they did not want to delete. Now they have 30 days to get them out of a "recently deleted" folder. I guess it makes sense but if you're trying to make room on your phone - don't forget to "remove" the deleted photos.