how to move icloud photos back to phone after factory rest

If you had iCloud Photos (Settings > [username] > iCloud > Photos > iCloud Photos) turned on before the reset, turning that option on again should result in them being automatically synced back to the phone. Also see: Set up and use iCloud Photos - Apple Support

If you didn't have that option turned on but did have an iCloud Backup, you would need to restore the phone by using the backup. See: iCloud: Restore or set up iOS devices from an iCloud backup