"Phone" isn't really a term that makes sense for the future. It's just a somewhat anachronistic bundling of microphone/speaker/digital radio/battery (and the tiny bit of logic needed for that to work together).
It does make sense to carry the things that comprise a "smart phone" (as above, +powerful cpu that can scale down to conserve power, gpu, screen/hud/display, camera(s), low-power local-area digital radio (eg: bluetooth), touchscreen (or drawing surface/digitizer), text-input (keyboard), gps, interface for connecting 4k+ display, possibly direct-attached storage), along with a headset, preferably wireless.
I just don't see why this should all be forced into one unit. I'm not sure how much power miracast would require -- but could it really be more than what the led-lit touch-screen uses? Because surely it'd be easier to have big battery+wlan/miracast/bluetooth/cpu stuffed in your pocket, and a small display+touch+bluetooth device on your wrist, with the option to pull out a phablet-sized hi-res touch-screen with it's own battery, but only miracast+bluetooth (maybe a gpu)?
The "smart stick" (the smarphone less the camera/screen/mic) could probably be made to fit more nicely in a pocket if there was no need for a display.
Shape it like a rod, add a powerful vibrator and the thing would even be dual-use ;-) (seriously, though - if it's intended to be kept in a pocket, a vibrator might make sense, as well as a couple of status leds).
The screen is going to be a bit clunky anyway (unless it folds/rolls up) - so no real issue to add a dedicated battery for it.
Maybe I should file a patent for "smart rod".