Whenever I get the 'Whatsapp' voice call and when I open the screen to pick it up , at that moment the phone automatically restart.
Update to latest stable OS ver 10 .
Sorry for the late response.
If you uninstall and re-install Whatsapp, does this instant restart behavior continue? Have you factory reset your phone since the update to Android 10?
If the answer to both of these questions is yes, ping me in the reply and we can log your phone to see what is going on.