On your Android smartphone you may have created contacts within the Contacts app that cannot be deleted. They are virtually read-only.
If you want to delete such a read-only contact in Android, you have to use the following procedure:
Unprotect a contact and delete it
1. Open the contacts app
2. Select the read-only contact.
3. Select the three-point icon in the upper right corner and choose "Show linked contacts" from the context menu.
4. Select "Unlink" and confirm the operation.
The disconnected contact can now be easily deleted as usual after you have removed the link.
A contact cannot be deleted whenever it is contained in and linked to multiple address books. By unlinking the contact as described above, the contact can then be removed from the address book without any problems.