Weather a PhD is a good option or not depends on what you want to do in life!.. It could be great if you want to be a professor or do research for companies or colleges.. or even work for the government (which might not be easy though). On the other hand, if you want to work for wall-Street, I would rather suggest a CFA designation, if you don't already have one. I assume you already have a MBA, right? If you don't, get that first. MBA is much more valuable than a PhD. But I assume you already have a MBA....

If you just have a bachelor's degree, you could even try Masters in Finance (MS Finance). But if you alreday have a MBA degree, it will be useless, unless you have a MBA degree in something other than finance.

But one thing is certain, before getting you PhD, try to gain some work experience. You'll go nowhere with a PhD in finance without prior work experience.

Hope that helps :)

Cheers!