Keep your phone on silent (whenever possible)
Unlike life in the West, Japanese tradition is heavily focused on groups of people rather than individualism. So, whatever you do, you should always take the feelings of the people around you into consideration. This is especially true when using your phone in public.
The Japanese don’t really like hearing loud noises in public places like subways or buses, so make sure your phone is on silent. If at all possible, don’t receive any phone calls while taking the bus. Instead, just send out text messages. However, in the event of an emergency, you’re free to do whatever you need to, within reason.