There are no exemptions to the rule of not using mobile phone while driving. Even doctors who are taking an emergency call while driving will be penalized.
If you get an emergency call while driving, the best thing to do is park the vehicle on the side and then talk. There is no penalty for this.
Talking on phone while driving is an offence because it puts you and the other drivers on road at risk, as your mind gets distracted and chances of accident increases. So, it is for your own safety and the safety of other drivers on the road, plus the pedestrians walking on the side.