A device used in many other devices that manipulate space-time. However on it's own it has its uses.
A phase controller generates a phase field, within which the phase frequency is changed as programmed in the device.
While it can in theory be used to travel to other dimensions, its real purpose is generally to control the phase in devices that allow for that.
It is an evolution of gravity controller technology.
It varies per manufacturer and species, but it generally involves rings of light.