Open the Contacts app
Tap and hold a contact
Tap Delete Contact
Repeat for each contact you want to remove
Open the Phone app
Tap Contacts
Delete contacts one by one from the contact card
Open iCloud.com on a computer
Sign in with your Apple ID
Open Contacts
Select multiple contacts using Command or Ctrl
Press Delete
Confirm deletion
Turn off Contacts sync in Settings if you want to stop contacts from returning
Go to Settings
Tap your name
Tap iCloud
Turn off Contacts
Choose Delete from My iPhone if prompted
Use a third-party contact management app that supports bulk delete
Back up your contacts before deleting them