How do I activate a ringtone on an Apple iPhone 5s?

Hello everyone. I am posting this question for an iPhone user who does not have an account. My father was given a new Apple iPhone 5s through his employer and he noticed that when people call him, the phone does not ring. How can he turn on the ringtone? He has a ringtone and alert tone set for everything on the phone, but when someone calls, the phone just vibrates. The vibrate setting is activated. Is there something else he needs to do?