How do I remove ALL PHOTOS from iPhone?
Your question doesn't full specify what you're wanting or what you've already tried, so I'm assuming you want to do this directly from your iPhone (as opposed to doing it while your iPhone is connected to a Mac/PC).

I'm also assuming you're just wanting to free up space and you've already backed up your photos. If so, you can follow these steps:


Open the Photos app on your iPhone
Tap on the Albums icon down the bottom
Tap on the Camera Roll album at top left
Tap on Select at top right (the word Select will change to Cancel)
Tap on the status bar at top of the screen (this will take you to the oldest photos in your Camera Roll
Now tap on the first photo (at top left) without taking your finger off the screen and while keeping your finger down gently swipe across the screen and then swipe down continuously - this will select all photos up to the point at which you take your finger off the screen
Tap on the Trash can icon at bottom right to delete all selected photos


NOTE: If you're doing this to free up space, then you will also need to remove your deleted photos from the Recently Deleted album (as photos are stored there for 30 days before actually being removed from your device). You can select the Recently Deleted album from the very bottom of the Albums screen in order to remove them from there and free up space.