Make sure its addons/phx/info.txt
- Not addons/phx/phx/info.txt or addons/addons/phx/info.txt
I don't know which file Meg provides, but I've seen one that has two phx folders (it should only have one).
If he fixed that, then it may already have included the addons folder, and all you were supposed to do is extract the file to <gmod root>, not <gmod root>/addons.