Do you mean you have a PhD in math and you want another PhD in math? I don't know, but say if you did the PhD in pure math and want a PhD in applied math, I would think it is possible. In physics for example, if you have a PhD in physics you it is possible to apply for another PhD in medical physics or in math. In fact, some graduate programs explicitly state that! See for example the math program in University of Maryland College Park, they say that you can apply to the math PhD even if you already have a PhD.
You will hear some people telling you that you can't or you can if you you want to go to a completely unrelated subject like from math to history, BUT: they have no idea what they are talking about or they just want to discourage you!
I suggest you contact to individual program (if they don't already same something about it in their FAQs section), pursue your dream even if it takes you years.
I feel passionate about this because I was in your situation years ago, and heard so much misinformation about the subject. People told me why would you want to take the same coursework again? Well, I will understand it even better! They say it is a waste of time; no it is not!