What is your advice on doing MA/M.Sc psychology after MBA in HR or is it better to take up Ph.D?

Doing a Ph.D would open up opportunities in HR consulting or teaching, teaching no doubt has great scope, these days, it depends if you would like to take that path. However if you are interested in HR as a career option, doing M.A/ MSc in Psychology will help you in your HR profession. You will be able to optimally use psychometric testing tools and other evaluation tools, to assess prospective employees, settle serious conflicts. Since the main role of HR is to liaison between the management and the employees, a degree in psychology will help, you can check out Industrial psychology, it may be a better match and will help more that a Ph.D in HR. Finally it is your decision, both lead to different career paths.