how can you tell if backup is complete
how can I tell if my contacts are backed up to icloud from my I phone
iPhone 8 Plus, iOS 11.0.2
If you're using iCloud, then your contacts will be both on the phone and in iCloud -- What does iCloud back up? - Apple Support.
If you're not using iCloud, then perform a backup -- How to back up your iPhone, iPad, and iPod touch - Apple Support.