Can a PhD answer this question?

You will need real analysis for the micro econ sequence nearly every finance PhD program requires (you will be using the Mas Colell book, so maybe take a peek at that to see if your math background is strong enough). You might have to take some of the macro courses, as well, where differential equations will be useful. For the econometrics, linear algebra will help since it will all be matrix algebra based. The more math you know the easier the program will be. Check out http://www.urch.com/forums/phd-business/ and search for the best math courses for finance PhDs, I'm pretty sure the topic has been covered multiple times. Good luck!