In phase two, you can gain access to the closed beta by simply hitting the "like" button on the game's Facebook page. That will give you access to a key generation tool, granting you a key to use on Steam. If you're already a fan, you still have access to the key generator. The announcement notes it's for a limited time, but a representative told Shacknews that caveat is to prepare for the open beta.
The beta features the competitive multiplayer and skirmish modes across six maps, along with the ability to play with teammates against AI. You can rank up to level 40, and customize your loadouts.
"After a successful first phase, we are delighted to be able to open the Closed Beta up to all of our Facebook fans and invite them to help us test and improve the game," producer Greg Wilson said in the announcement.