Finance at that level can be very heavy in math and statistics. As an undergraduate, you may want to continue math and statistics beyond the usual business major requirements. For example, multivariable calculus, linear algebra, real analysis, and probability theory may be helpful.
Understand that goal is like saying “I am going to play pro ball” or “I am going to be a movie star”. It happens- but much more rarely than you may realize.
Also remember that a PhD is a research degree, and that (to quote from Stanford): "It is particularly important to realize that a PhD in finance is not a higher-level MBA, but an advanced, academically oriented degree in financial economics, with a reflective and analytical, rather than operational, viewpoint.
My gut feel here is that transferring is a reach, and you are already at a very good university. I think that getting good internships could help you quite a bit. Also, I agree with @ucbalumnus that having some advanced math classes might help you as well.
I was a math major. As a graduate student I took a course in econometrics. It was the only non-math course that I took as a graduate student. I liked it quite a bit. However the amount of math that I needed to do well in econometrics was significant. Even as a math major I spent a few hours on a couple of Saturday afternoons going over details of linear algebra to make sure that I was solid in the math that was used in this course. I can also see how a solid background in probability and statistics would be quite useful for an advanced finance degree.