There are three ways to hide photos on an iPhone. They protect against very different things.
1. The Hidden album in Photos
Select a photo, tap Share, then Hide. It moves to the Hidden album, which since iOS 16 is locked behind Face ID. This is fine against a glance over your shoulder. It is not encryption: the photos still sync to iCloud Photos as normal, still appear in backups, and anyone who can unlock your phone with your passcode can open the album.
2. A locked note or a locked folder
Notes can hold photos behind a password. It works, but it is clumsy for more than a handful, and the note still lives in iCloud in a form Apple can read.
3. An encrypted vault app
A vault app encrypts each photo on the phone with a key only you hold, then stores the scrambled file. Without the key, the file is noise. In Vaultpod the key comes from a pattern you draw; the photos can be backed up to your own iCloud, still encrypted, and brought back with a recovery phrase.
Which one?
Hidden album: casual privacy, zero effort. A vault: when you want the photos unreadable to anyone else, including anyone with your passcode, and still safe if the phone is lost. After importing, a vault app offers to delete the originals from Photos; say yes, or they are still in the library.