With added VR glasses, you can move around in a virtual underground cavern, and other worlds, just by moving around holding your phone. Pin-point accurate GPS will do the rest.
And when people call you, their avatar will appear in front of you, speaking lip-synchronized.
To avoid bumping into other people, the phone will display them as cones (unless they have an avatar ofcourse)

One day I ran through the cleft for the fiftieth time, and found that uru held no peace for me anymore.