If you are talking about Camera Roll photos, try this.
Import all Camera Roll photos to your computer.
Delete all photos and video from camera roll.
Check if you free up storage memory.
Make an album/folder and sync them back to your iPhone.
Keep and backup the photos on your computer because these are the original files. iPhone syncs an optimized version of these photos. Are smaller that the original ones.
Tell to your friend to do the same. Use you Camera Roll as a digital camera card. (Copy to computer and empty the card). You will free up space from your iPhone and from iCloud backup (if you use it). Your iPhone is not a storage/backup device.