If the PhD program you're interested in is very quantitatively demanding, say, finance or operation research, it's almost a requirement to have had linear algebra, calculus. At the very minimum, several college level math classes will be needed. That's why many top programs actually admit students who have had a PhD in physics, math or engineering. These people are very good at building models. Check with the specific program to see if it is more math oriented. As for academic background, I heard you better have had published scholarly work before applying. | 
