Glossary definition of 'Phantom power'A DC voltage applied equally to both signal lines of a balanced audio connection. Its primary use is to power condenser microphones although it is also used to power DI boxes etc.
Phantom powering is now standardized in IEC 61938 which defines both 48V and 12V phantom power voltages. Both signal conductors are at the positive voltage and are used relative to ground (XLR pin 1). 48V phantom power is fed through current limiting resistors, usually 6.8kΩ and is usually only capable of supplying a few 10s of milliamps. Since the voltage is the same on both legs, there should be no potential difference across the coil of dynamic microphones plugged into an input with phantom power enabled, so it should do no harm.
Computer sound cards, laptop microphone inputs, and some consumer portable products designed to use cheap electret microphones often supply between 3 and 5V DC to power the electret FET amplifier. This is not the same as phantom power, and these microphones may not survive if connected to a 48V phantom power input.