You might be using WhatsApp on the laptop or your PC via the browser or the desktop app, but the messaging platform only works when the primary device, in this case, your smartphone, is connected to the Internet and is turned on. So, if you lose your phone or it gets stolen, you will not be able to use the messaging app anywhere else.
WhatsApp has mentioned a few steps that you can follow if your smartphone is lost or stolen to stop other people from being able to access your WhatsApp account. Keep in mind that remote deactivation of the WhatsApp account is not possible so you need to make sure you follow these steps.