How to free up iPhone space without deleting your photos
Short answer
You can keep every photo and still free a lot of space: compress 4K videos to 1080p, turn on Optimize iPhone Storage for iCloud Photos, offload unused apps, and merge exact duplicates, which removes copies but no moments.
Shrink videos instead of deleting them
Videos are most of the space in a full library, and they're the easiest thing to shrink. A 4K clip converted to 1080p keeps the moment and looks the same on your phone. See how to compress a video on iPhone.
Let iCloud hold the originals
With iCloud Photos and Optimize iPhone Storage on, full-size originals live in iCloud and the phone keeps smaller versions, downloading the full one when you open it. Settings › [your name] › iCloud › Photos. It needs enough iCloud storage for your whole library.
Remove copies, not moments
Exact duplicates are the one thing you can delete without losing anything, since another copy stays. Use the Duplicates album in Photos, under Collections › Utilities. See how to delete duplicate photos.
Look outside Photos
- Offload apps you rarely use: Settings › Apps › App Store › Offload Unused Apps.
- Remove downloaded episodes and playlists you've finished.
- Clear Safari's website data: Settings › Apps › Safari.
Doing it with SlashPhotos
SlashPhotos can shrink as well as delete. It makes 1080p copies of large videos and compresses photos to HEIC at the lowest quality that still passes a strict visual check, keeping dates, locations, HDR and Portrait depth. You see both versions before anything is replaced.
Questions
Does Optimize iPhone Storage delete my photos?
No. The originals stay in iCloud and the phone keeps smaller versions, downloading the full one when you need it.
Is it safe to compress photos on iPhone?
Converting to HEIC at a high enough quality looks the same to the eye. Check the result, and keep originals of anything you might print large.