Isn't F1 visa valid for 5 years? 2 years masters + 3 opt. Why do you have to renew?
PhD students usually exceed 5 year mark. My wife after joining PhD never got stamped at Indian embassy. She came here as h4 and converted her visa to f1 to join PhD program.
My wife is going to do that in January when we are going to visit our family in India. She is post doc now at university.