Desktops remain more capable than anything portable, in particular phones. The mobile machines do one thing, and that is, be mobile.
Desktops will always be more powerful than phones, or even laptops. It's a matter of power demands and physical space; anything you can fit into a laptop, you can fit four of in a desktop. What has changed in the last decade or so, the reason desktops are in decline, is that laptops have become way more than powerful enough for most of the tasks that most people perform, and they've gotten a lot less expensive.