What is the best way to delete all images from camera roll. I am selling my phone and don't want to try deleting them one at a time, nor do I want to leave them.
Connect the iPhone to a Mac or PC running iTunes and do a complete Restore to factory settings. This will wipe out all media & data and install the latest version of iOS for that device.
If you don't have a Mac or PC for this task, on the iPhone itself, you can go to Settings > General > Reset > Erase all content and settings.
NOTE: Be sure to disable Find My iPhone if you have it enabled, and logout of any iCloud services.