The fastest way to delete pictures from your iPhone’s camera roll is to go to the “Moments” section in your Photos app and use the select button to delete whole days at a time. In your Photos app, go to Years -> Collections -> Moments and tap the “Select” button in the top right. Now you can select a whole day with another select button, or individual pics from within a day by tapping on each photo. When you have selected everything you want to delete tap the trash icon.