Hey! Tis a pretty good point, strictly speaking the armoured phantoms / bound skeletons / fetid zombies are intended purely to be 'the npcs north of fort'
In dev they were called Zemouregals Phantom, Skeleton etc but it was weird to have them named that before you saw Zemouregal, though that name is probably more appropriate.
When we made those however we did add clusters for 'phantoms' similar to tasks that are just 'ghosts' / 'zombies' / 'skeletons' but there simply wasn't enough phantoms in game to justify enabling the task.
If/when we get some more in-game we can absolutely enable it which I would assume would encompass hermod too.
TLDR: Hermod is a phantom (i think). Armored phantoms is a bad name, but refers to Zemouregals ones. 'Phantom' slayer tasks may very well get added in the future.