Worry not about silly questions like "Why not just carry the phones with you?" or "Should we call the police?" Instead, let's just take a brisk look at what's going on here and move on, quickly.
The swinging apparatus is a webcam and the three phones are suspended beneath its swaying gaze. The rest of the servors, cables and electronics control ever facet of those three phones, save the tiny voices in Bak's head.