It is not advised to talk to anyone on your phone whilst driving if at all possible as there will be a certain amount of your concentration devoted to that call which has been taken away from driving.
If you do need to use your phone then you need to make sure that you have a quality blue tooth device installed to allow you to make and receive calls hands free.
Many car stereos now have blue tooth built in which once paired with your phone, will allow you to speak to the person on the other end of the phone using the inbuilt mic and car stereo speakers.
Blue tooth calling devices can be picked up relatively cheap now but not only is it the legal way to use your phone, could stop you having an accident.
Many accidents happen every year whilst people are talking on their phone but with Blue tooth, this number is slowly decreasing.