Phantom power is DC (or direct current) used to power certain microphones, the UX2 and KB37 offer 48-Volt signal to a condenser microphone by connecting it to the XLR input on the unit.
The UX1 does not have phantom power, if you have a microphone that requires such power you will need to get either a standalone microphone preamplifier or one that is built into an audio mixer's input channel. Also available are stand alone phantom power boxes. (A good example of this device is the Rolls PB23 Phantom Power Supply).
Phantom power is not harmful to mics that don't need it. If a mic does not need phantom power it will ignore the 48-Volts being sent the the microphone.
Even with the Phantom Power on, your UX2 or KB37 can have both a mic that requires Phantom Power and a mic that does not require Phantom Power.