We present a 3D user interface for collaborative manipulation of three-dimensional objects in virtual environments. It maps inertial sensors, touch screen and physical buttons of a mobile phone into well-known gestures to alter the position, rotation and scale of virtual objects. As these transformations require the control of multiple degrees of freedom (DOFs), collaboration is proposed as a solution to coordinate the modification of each and all the available DOFs. Users are free to decide their own manipulation roles. All virtual elements are displayed in a single shared screen, which is handy to aggregate multiple users in the same physical space.