A-ha, so you are a JP1-er. Phantom keys are keys that don't really exist. Even though a particular remote may only have, let's sat, 40 buttons, it could in theory handle many more. Phantom buttons use button codes for which there isn't really a physical button.

We use phantoms to program key moves for functions that we only want to use in macros, and never need to use via a real button, such as discrete power codes, etc

Rob