As a general rule, you will be selected for the Ph.D programme in a reputed university if your marks secured in the Masters degree in the stream for which Ph.D is sought is not less than 55 percent. A concession to the extent of 5 percent is allowed for SC/ ST, Backward classes, Women candidates from the weaker section of the society etc
Since you are not fitting to the reserved category the only option left before you is to continue M.Phil course from a recognise university and make an attempt to secure at the least the minimum marks ( ie 55 percent at least) in that examination.
Once you achieve the threshold mark in M.Phil in your chosen stream, you will be considered for your Ph.D programme provide you clear the entrance test test set for this purpose apart from the interview of the panel experts assessing your passion, interest, your research ability and other capabilities.,
While filling up your application form, you may indicate the area where you are interested for perusing your Ph.D.