How do I stop call log syncing back after iOS erase and install? I have been having this issue for quite some time now:

After I restore my iPhone to factory settings and signed in my iCloud account, the call logs would come back mysteriously, even ones dating back a few months that I have deliberately deleted.

This is really scary if you think about it.

There does not seem to be anyone else asking this particular question.

How may I solve this problem?
You simply can't. Not yet anyway. Apple hasn't added a switch for it so as long as you connect to your iCloud account, the call log is going to sync.