I think the point of the person you're responding to, was that if you use the selenium interface with PhantomJS, you can change your testing browser to Firefox,

I think the point of the person you're responding to, was that if you use the selenium interface with PhantomJS, you can change your testing browser to Firefox, Safari, etc with very little work on your part. i.e start with Phantom/Selenium, then test with the rest when you're ready.