Open the Contacts app
Tap the duplicate contact
Tap Edit
Scroll down and tap Delete Contact
Confirm Delete Contact
Repeat for each repeated contact
Open the Phone app
Tap Contacts
Use the search bar to find duplicates faster
Delete each duplicate contact one by one
Open Settings
Tap Contacts
Tap Accounts
Check each account syncing contacts
Turn off contact syncing for duplicate sources
Open iCloud.com on a browser
Sign in with your Apple ID
Open Contacts
Select duplicate contacts
Delete the duplicates
Sync your iPhone again
Use a third-party duplicate contacts app from the App Store
Scan for duplicates
Merge or delete repeated contacts
Back up your contacts before deleting anything