Yes, a Master's degree from IGNOU is acceptable for admission into Ph.D. courses in top universities. The eligibility criteria for some of the top universities in India which offer Ph.D. courses are as follows.
Indian Institute of Science Bangalore:
NIRF has ranked the Indian Institute of Science Bangalore 1st in the university category in 2020.
The eligibility criteria for pursuing a Ph.D. from the institute in any discipline is a master’s degree in a related field from any recognized university.
Jawaharlal Nehru University:
Situated in New Delhi, JNU has been ranked as the 2nd best university in India by NIRF 2020.
The required eligibility for Ph.D. courses is a master’s degree in a related discipline with a certain cutoff from any recognized university.
Banaras Hindu University:
According to the NIRF 2020 BHU is ranked 3rd among Indian Universities.
Students with masters from any recognized university in a related discipline can apply for the Ph.D. courses at BHU. The institute also conducts a test to select the students for admission.
Generally, the eligibility criteria of most of the top universities state that any qualification recognized by the Association of Indian Universities New Delhi which is equivalent to a Post Graduation’s Degree awarded by UGC recognized University/Institutions. This means a master’s degree from IGNOU will be acceptable for top universities for Ph.D. because IGNOU is recognized by UGC. There might be some exceptions in college, for example, the eligibility criteria of colleges also depend on the course in which the candidate seeks admission. Therefore, a candidate should check the eligibility criteria of a college before applying for the same.