how do i delete all photos off my iPhone?

So I ran out of storage space on my phone. When I go to Settings>General>iPhone Storage, my Music and Photos app takes half of the storage. I sync frequently on my computer and I don't use iCloud for music and photos (when Apple lets me avoid doing so for both), so all my music and photos are on my computer and it's fine to delete all of that data from my phone.

When I click on "Music", I can delete the entire app and data - Great - Many gigs recovered! But when I click on "Photos", I cannot delete anything - Why the H not? When I open the Photos app, I can delete a photo one at a time - Fine. But I want to select ~all~ of them and delete them in one stroke, like I just did all my music - This I cannot easily do. Matter of fact, I can't figure out how to do it at all. Can someone explain how on the iPhone itself to delete all of the photos without selecting them one at a time? There are just too many to manually do this. Please tell me there is an easy way to do this without having to 1) sync the phone; and 2) erasing the phone - Please. I know for a fact that using computer-sync to remove music and photos is not always complete and some data gets left on the phone, which the computer then doesn't know about and it cannot be removed via computer-sync.

Thank you .. Rob