Sorry, mate, but what they're all hinting at is that it's the external display that acts as input here: your laptop's graphics card renders a frame, it sends it to your laptop's video outputs (HDMI being one of those), this image gets transferred to a display device (which receives it as an input) and gets displayed. Your monitor, for instance, doesn't produce any images on its own, it only displays what it being sent to it (e.g. by your laptop) - and you use your laptop's HDMI port exactly for that, to output something for other devices to display.
Now, your phone's HDMI port works exactly the same way: it outputs whatever it is you see on your phone's screen (so that you can hook your phone up to a TV and enjoy Android in its full HD glory), and it's not meant to receive any signal.
So that's why there's no point in connecting your laptop's HDMI to that of your phone: they both are trying to transmit their own signal to some external display, but neither can act as such. Well, not by using conventional means, anyway.
