Check if your contacts are synced with iCloud
Go to Settings
Tap your name at the top
Tap iCloud
Turn on Contacts
Open the Contacts app and wait for sync
Restore contacts from iCloud.com
Sign in to iCloud.com
Open Account Settings
Scroll to Data Recovery
Click Restore Contacts
Choose an archive and restore it
Check other accounts
Go to Settings
Tap Contacts
Tap Accounts
Open each account
Turn on Contacts for the account
Restore from an iPhone backup
Go to Settings
Tap General
Tap Transfer or Reset iPhone
Erase all content and settings
Set up iPhone again
Restore from iCloud backup or computer backup
Restore from a computer backup
Connect iPhone to a Mac or PC
Open Finder or iTunes
Select your iPhone
Choose Restore Backup
Pick the most recent backup
Check hidden contact groups
Open the Contacts app
Tap Lists or Groups
Make sure all contact groups are selected
Restart your iPhone
Turn off iPhone
Turn it back on
Check Contacts again
Update iPhone
Go to Settings
Tap General
Tap Software Update
Install any available update
Check SIM contacts
Go to Settings
Tap Contacts
Tap Import SIM Contacts
Contact Apple Support if contacts are still missing