无法并行运行Selenium PhantomJS实例

I'm using Selenium's node.js API to run PhantomJS instances against a series of web pages. The code I use to execute the actions on the pages work fine, but it seems only one instance of Selenium/PhantomJS can run at a time. This function is called multiple times from the same module and steps through pages in a webshop where the pagination is handled client side (which is why I need the Selenium/PhantomJS environment - to extract data from each page).I'm using Selenium's node.js API to run Phantom