FetHead Phantom is a FetHead version specially designed for condenser microphones. It works very well with electret microphones like the countryman or an AKG C1000. These are microphones which consume little power, FetHead Phantom also works great on "real" condenser microphones like a Neumann U87, AKG C414 etc. FetHead Phantom is also an indispensible tool for mobile recording and a real upgrade for Camera microphone preamps.
"What is the difference between the regular FetHead and the FetHead Phantom?"
A regular FetHead is designed for dynamic microphones and ribbon microphones, it has a relatively high impedance of 22k which allows the microphone the microphone to operate at "no-load" condition. A FetHead Phantom is designed for for Condenser microphones or other Phantom powered devices, it passes Phantom Power to the microphone.
"Can I use the FetHead on the preamp side of the signal chain?"