Source: http://gizmodo.com/5974276/why-4k-phones-arent-such-a-bad-idea
If people are working on UltraHD screens for mobile phones, Raj would know about it, as Qualcomm builds chips for virtually every mobile device manufacturer you can name. 1920 x 1080 pixels (1080p) on five inch screens—which are popping up like crazy on new high-end phones) have 440 pixels per inch. You couldn't see those pixels if your eyeballs were pressed to the glass. So, I asked him what the point could possibly be. It's just a pointless manufacturer pissing contest, right?
Raj's answer was that sure, above 400 PPI or so, it's not really about how many pixels the screen itself can display, what's important is how many pixels the phone is capable of pushing, as in CPU and GPU horsepower. It's because of things like Miracast, where you can wirelessly push video and audio to your TV. If these upcoming phones with the superfast Snapdragon 800 processor can shoot 4K UHD video, wouldn't it be great if you could push that directly to your 4K UHD TV? Damn right it would. And there's certainly room to go well beyond 1080p on larger tablet screens.
We really hope that phone manufacturers don't waste their time, energy, and endless marketing dollars on pushing beyond 440 PPI displays for phones. Until we all have our eyes replaced with robotic cameras, their efforts would be better spent on making screens more efficient. If you look at your phone's battery stats, the screen is always the biggest devourer of juice, often by a factor of three or four. That said, if chip makers like Qualcomm are eager to push beyond 1080p into 4K video recording, even 8K video, bring it on.