v1.0.x used to leverage dnode to communicate between nodejs and phantomjs. This approach raised a lot of security restrictions and did not work well when using cluster or pm2.
v2.0.x has been completely rewritten to use sysin and sysout pipes to communicate with the phantomjs process. It works out of the box with cluster and pm2. If you want to see the messages that are sent try adding DEBUG=true to your execution, ie. DEBUG=true node path/to/test.js. The new code is much cleaner and simpler. PhantomJS is started with a shim which proxies all messages to the page or phantom object.