I was going to rant endlessly about phones and desktops having rather different uses and capabilities. For a given level of technology, I suspect that I really don't want to try extracting 300 watts or so of heat from a hand-held device if I value my skin lacking burns.
But you get the upvote of the day for pointing out the rather more prosiac and obvious difference. I have absolute authority over my desktop, and I say what goes. On the phone? Pffft. It's an endless pain in the backside to simply retain what little control is there.