Check if Contacts are turned on in iCloud
Open Settings
Tap your Apple ID name
Tap iCloud
Turn on Contacts
If prompted, choose Keep on My iPhone
Restore contacts from iCloud.com
Sign in to iCloud.com
Open Account Settings
Scroll to Data Recovery
Select Restore Contacts
Choose an archive and confirm restore
Restore from an iPhone backup
Open Settings
Tap General
Tap Transfer or Reset iPhone
Tap Erase All Content and Settings
Set up the iPhone again
Choose Restore from iCloud Backup or Restore from Mac/PC Backup
Restore from a Mac backup
Connect iPhone to Mac
Open Finder
Select your iPhone
Click Restore Backup
Choose the most recent backup
Confirm restore
Restore from a Windows backup
Connect iPhone to PC
Open iTunes
Select your iPhone
Click Restore Backup
Choose the most recent backup
Confirm restore
Check email accounts linked to Contacts
Open Settings
Tap Contacts
Tap Accounts
Open each account
Turn on Contacts
Refresh Contacts
Open Contacts app
Pull down to refresh
Wait for sync to complete
Restart the iPhone
Turn the iPhone off
Turn it back on
Update iOS
Open Settings
Tap General
Tap Software Update
Install the latest update
Contact Apple Support if contacts are still missing