Check the phone’s Trash, Recently Deleted, or Bin folder in the Contacts app
Restore contacts from your Google account on Android
Restore contacts from your iCloud account on iPhone
Sync contacts again by turning Contacts sync off and on
Check other linked accounts such as Gmail, Outlook, Yahoo, or Exchange
Restore from a recent phone backup
Use the SIM card contacts option if contacts were saved there
Check messaging apps or call logs for saved contact details
Use a data recovery app if no backup is available
Contact your mobile carrier or device support if needed