WARNING : No target specified, deploying to emulator

I had another developer tool opened (Chrome Inspect) and it "ate" the connection. In my case, just closing the Chrome Inspect panel and running ionic run android worked.

I solved the problem.

Here is what I did: I typed into the command line: adb devices (located in the "platform-tools" folder in the Android SDK) which returned me an empty list.

So I installed my phone's drivers, which I downloaded from the vendors homepage.

Now the list contains my device and the app is started on my mobile phone.

I had a different problem, with a very simple solution.
When plugging in your Android device for the first time, it'll ask you to trust the computer's certificate. That popup screen disappeared on me, as I was just getting a call.

Simply unplugging/replugging your phone and accepting your computer's certificate should do the trick!

Once you've enabled your device for debugging, make sure to turn on usb tethering on the device;

Settings > Tethering & Networks > USB tethering

This fixed the problem for me.