Ph.D

You are eligible to seek admission in Ph.D after obtaining MCA degree from a recognized university.

Hello,
If you want to pursue Ph. D. then you should have a Masters degree. If you are from arts field then you can apply for NET exam to complete your dreams. If you are from commerce field then you have a good option available to pursue it from IIT or IISC, for that you have to apply for its entrance exam i.e. IIT JAM and you can also do it from NIT.
Now, the decision is yours.

The eligibility criteria for PhD in major universities is MA in the relevant discipline from a recognized university/institution with 60% marks in aggregate or equivalent and BA with minimum 60% marks and NET qualified. However, some university allows even students with 55% in MA. Therefore, you may do PhD in universities where you meet the admission criteria.

I have shared below the complete details about your query.
http://csirhrdg.res.in/jrfsrfra2.htm

Please refer to attached link for list of university which allows CA to pursue PhD:
http://resource.cdn.icai.org/26417bos15829.pdf

Yes why not. However, you must have completed PG.

Delhi University, Bombay University and ISB Hyderabad are one of the best for PhD in India.