If you want to back up or transfer your wallpapers to another device, you can use iCloud or iTunes. To back up your wallpapers using iCloud, go to Settings > [your name] > iCloud > Photos and turn on iCloud Photos. This will upload your photos and wallpapers to iCloud and sync them across your devices. To back up your wallpapers using iTunes, connect your iPhone to your computer and open iTunes. Click on the device icon and select Photos. Check the box next to Sync Photos and choose where to sync them. Click on Apply.