That's the point: Ara is a phone that can be rebuilt in many different ways, and reassembled easily. It's kind of like a smartphone made out of Legos.
It's a radically different way to think about how we use our phones. Instead of buying a phone based on specs, Google wants you to configure Ara according to what you want to do with it. That could mean switching in better camera when you're heading to a wedding, or loading up a bigger battery in preparation for a business trip.
Ara was developed by Google's Advanced Technologies & Projects division (ATAP), which works on some of the craziest ideas at the company — like Project Jacquard's touch-sensitive fabric.