It really depends on the program requirements. If his studies were in English, he might not need an additional language test.
anyway, if he does, it should be either IELTS Academic module (not General) or TOEFL, which is preferred. Some institutions accept only TOEFL and for some IELTS is OK too.
Browse the PhD programs in different institutions and see what exactly is required (minimum GPA, score, recommendations, letter of intent etc.)
