A phantasm has been defined as a "fantastic sequence of haphazardly associative imagery, as in dreams."
But in terms of the Tall Man -- Angus Scrimm's iconic cinematic Bogeyman -- a phantasm can certainly be defined as a nightmare.
In the movie's sad "real life," depicted momentarily at the film's conclusion, Mike's beloved older brother Jody is -- like the boy's parents -- dead and gone. Mike is pretty much alone, at least in terms of biological family.
I have long subscribed to the belief that many of the scariest "monsters" in horror history (on both TV and in film) are those beings that don't actually kill their victims.
Technically, it's called Gerontophobia. And no, it's not nice, and it's not really fair...or even remotely rational.
As far as horror bogeymen go, an important rule is this: the right tool for the right job.