Normally you could close the pop-up by click on the (x) on the top right of pop-up page. Have you tried to do that?

I get that too. There is no way out of it. I can't remember if there is an x or an x that doesn't work. It is really annoying.

Without being logged in, can you click on the self serve menu, click the drop down and then click billing and then login? Does that by pass the phone upgrade screen? 

Also try clearing your browser's cache.