I had to download Android Studio, get the right SDK, emulator, etc, but finally got this up and running, and I got nothing. No data sent. Turns out, an emulator connecting on localhost doesn't work so well.
However, changing to 10.0.2.2, as this Stack Overflow below suggests, worked just fine. I sent a much longer string through to the PHP server you created and it echoed okay. Give it a try.
stackoverflow.com/questions/38668820/how-to-conne…
Edited to add: I had to give the appropriate permissions in the manifest. I assume you already did that. I also had to shut down my web server since that was bound to port 80 already. I assume you did that, too.