I know that phantom power means transmitting the power on the same wires as the input/output signals. There are phantom power microphones that have an included amplifier and are conected using just 2 wires.
The key is to provide adequate separation between the DC power voltage and the ac signal, using RC, or L(choke) C filters.
Also there are antenna amplifiers powered on the coax cable, and the amplifiers used in the long range transmission (wire) telephone systems were powered through phantom circuits.