<p>Every school has their own requirements for admission to the PHD program, so I suggest you start visiting the school website and look at their PHD admission pages.
On the other hand, every Math major to my knowledge has to take all the Calculus series form 1 to 3, plus linear algebra, and other higher math classes. Then again that depends on the undergraduate school you are attending.
So, whatever undergraduate institution you are going to attend has planned for math major, that is what you have to take to graduate.
In addition, visit the web page of the graduate schools that you are interested in, and see their graduation requirements for Maths majors;
Example:
<a href=“Graduate”>http://math.mit.edu/academics/grad/</a>
or
<a href=“Ph.D. Programs - Mathematical Sciences - Mellon College of Science - Carnegie Mellon University”>http://math.cmu.edu/graduate/PhDprogram.html</a></p>
<p>Best of luck to you.</p>