There are many ways to choose your university such as fees, the ranking of the university, which state it is located and scholarships. My suggestion is to choose your research focus and write academic papers. In the US, PhD in Commerce admission into the university depends on what you want to study (your area of research) and your already completed research papers. You can begin your research by searching online for US universities offering PhD in Business Administration. One example is University of California Los Angeles (https://www.anderson.ucla.edu/degrees/phd-program/admissions#app-req) .