The phone really brings nothing to the table.
Perhaps not for you. I know plenty of people who go out a lot for business meetings and don't need to take a full laptop any more, because they can get any urgent messages via their phone or other mobile devices. In our household we often use a phone or tablet to get directions and travel news if one of us is driving but has a passenger with mobile Internet. Sometimes it's just nice to get news that your friends got engaged or someone's baby arrived safely when you're out, and mobile social networking apps can tell you. Sure, you could also do all of these things with a laptop, but only if you left it turned on all the time, and it still wouldn't fit in your pocket.