I lost passwords that were previously saved

You have turned off iCloud Keychain or deleted the saved passwords How to find saved passwords and passkeys on your iPhone - Apple Support ( in that case passwords can't be recovered ) or if you signed off Apple ID from the single phone the passwords will be gone .

In case if another Mac / iPad was always signed in with same Apple ID and password on the same network , turning on icloud keychain will sync those passwords .

iCloud Keychain keeps your passwords, passkeys, and other secure information updated across your iPhone, iPad, iPod touch, or Mac. Set up iCloud Keychain.

Passwords are always synced by turning iCloud Keychain , however the passwords are encrypted but not backed up with iCloud , what does iCloud back up is explained in the article Back up your iPhone, iPad or iPod touch to iCloud - Apple Support (IN)

You can use iCloud to back up your iPhone, iPad or iPod touch. You can customise which apps and data are backed up.

For more information about what is included in an iCloud backup, see the Apple Support article What does iCloud back up? To learn about managing your backups, see View and manage iCloud device backups.

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Restore from an iCloud or iTunes backup: If you regularly back up your iPhone to iCloud or iTunes, you may be able to restore your Keychain data from a previous backup. To do this, go to Settings > General > Reset > Erase All Content and Settings, and then choose "Restore from iCloud Backup" or "Restore from iTunes Backup" and follow the prompts. Keep in mind that restoring from a backup will erase all data on your iPhone and replace it with the data from the backup .

No not possible to back up the password using iCloud back up or using iTunes .

If they used a Mac then password can be exported from Mac and imported in iPhone only when iCloud Keychain was set up on both .

If you've lost passwords that were stored in the Keychain on your iPhone, there are a few things you can try to recover them:

1. Restore from an iCloud or iTunes backup: If you regularly back up your iPhone to iCloud or iTunes, you may be able to restore your Keychain data from a previous backup. To do this, go to Settings > General > Reset > Erase All Content and Settings, and then choose "Restore from iCloud Backup" or "Restore from iTunes Backup" and follow the prompts. Keep in mind that restoring from a backup will erase all data on your iPhone and replace it with the data from the backup.
2. Check other devices: If you have other Apple devices that are signed in to the same iCloud account and have Keychain enabled, your passwords may be stored on those devices. Try checking your passwords on your other devices to see if they are still there.
3. Check if you are logged in to the device with the correct Apple ID. If not. Log back in with the correct Apple ID

Are you logged in with another Apple ID? That may be one of the reasons.