If you use iPhone for mostly browsing, the first place to look to regain more free space is Settings. Tap on Safari, then tap on Clear History, and tap on Clear Cookies and Data. This will remove your browsing history and your login details.
iMessage is also one of the biggest occupiers in your storage. Backup to iCloud also includes message cache, which means if you try to backup, clear message, and restore messages, the cache will also restored and you still don’t have your free space return. To solve this, you can remove it using iBackupBot.
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