Delete unused apps
Offload unused apps
Clear Safari history and website data
Remove large message attachments
Delete old photos and videos
Use iCloud Photos with Optimize iPhone Storage enabled
Empty Recently Deleted in Photos
Delete downloaded music, podcasts, and movies
Remove offline files from apps
Clear app caches where available
Review and delete large files in Files app
Delete old mail attachments
Reduce message retention settings
Update iOS to the latest version
Restart the iPhone after cleanup
Check storage usage in Settings > General > iPhone Storage