The common definition of mobile device is phone or tablet. The common definition of laptop is computer. These despite the fact that phones and tablets are computers and despite the fact that laptops and even desktops can be moved. It’s pretty easy to find lots of examples of the common definitions. Here’s a good one: https://en.wikipedia.org/wiki/Mobile_device
The question of whether definitions matter when one sub-category or subset is a minority or majority... I’m not sure how to answer that. Why would a definition stop mattering just because something different is a small subset? I must assume that a categorical term includes everything in the category. If you don’t mean everything in the category, then don’t use the term that refers to the category. If you mean phone, then say phone. ?? Right? I’m confused why you would argue anything else.