Some steps you can take to make sure you're doing it right:
Look inside the phx folder. Do you see a text file named "info", along with folders saying models materials, etc? If so, you've done it right.
If you see more folders inside, not named materials, models, or anything like that, then take those folders and check for an info file. If it exists, take the folder and put it into your addons folder.
Make sure to restart your game. Addons cannot be installed while the game is running.