Right now I don't really think there's much of an argument for Green. Phaneuf is the better defender by a huge margin, and Green's past two seasons he has been scoring at a pretty abysmal rate.
Basically, what you're asking is, "Do you think Mike Green will return to 70 point form?" because 2008-2009, 2009-2010 Mike Green is an entirely different beast than 2010-2011, 2011-2012 Green. Phaneuf is considerably better than the latter, but the former is one of the most dominant forces in the league (even if he's mediocre defensively).
I'm not the biggest fan of Phaneuf. In him I see a player with a lot of tools, but without the intelligence to really take full advantage of them. That being said, I think he's a significantly better defenseman than the Mike Green we've seen lately. The Mike Green who is the best offensive defenseman in the league has an argument, and with the numbers he was putting up I'd say it was a pretty good one, but he's not that guy right now.