If you are doing MSc in Physics then if you wish to become a Theoretical Physics, then going for the PhD is the only way out to make yourself established as a Theoretical Physicist in the academia. Now if you wish to go for PhD then the best choices for PhD are provided below-

• TATA INSTITUTE OF FUNDAMENTAL RESEARCH
• INDIAN INSTITUTE OF SCIENCE, BANGALORE
• INTERNATIONAL CENTRE FOR THEORETICAL SCIENCES, BANGALORE
• TIFR-HYDERABAD

For more information regarding Physics as a career consider the link below:

https://www.careers360.com/courses/physics-course

I hope this helps. Wish you a great eve!