The Cinetics miniSkates Pro Phone / Small Camera Dolly & Joby Ballhead Kit, from B&H, completes the miniSkates dolly with an adjustable (and affordable) ballhead that would enable an attached phone or camera to be movable.
The dolly is an assembly made specifically for phones and small cameras. The assembly features miniSkates, which are the smaller of the two types of Cinetics skates, to better support lighter loads. A phone or camera can be attached directly onto the dolly top plate, but the phone or camera wouldn't be too free to pan and tilt. The Joby ballhead enables full 360° panning and 90° tilting. A part of the head is a quick-release plate that you can attach underneath your phone or camera and then conveniently just slide onto the head.