Dear Rupalee,
Just inform him politely that people dont like the way he is speaking in the phone. moreover you MD dont like that. Convey the message to him.
In organisation an HR should not differentiate between senior and junior. you may have respect with the seniors but your organisational policy has to be downloaded to each and every employee of the organisation.
Still he is doing the same it is because of the EGO what the person has. in this case ask every employee to ask him to speak low. if every one is questioning he will be silent for sure. (Hope you have seen the naukri Advertisement - HARI SADU, H - Hitler, A - aragont, R - Rascal, I - Idiot). use similar strategy.