I noticed a common complaint about spiritualist is that it seems too much like a summoner. I think maybe a good direction for this class to go is like an unbound shaman or the aetherurgist. Instead of being bound to one phantom alone, a spiritualist can be temporarily bound to multiple phantoms than can be "deployed" and each triggers a spell if a certain condition is met. Then again this is a bit of a far cry from the original concept, but I think it might be worth considering. Another way to apply it is if your main phantom can recruit other phantoms via call spirit and those phantoms can be temporarily bound for a time and then deployed. The nature and mechanics of these phantoms depends on your main phantom, but at high enough levels you could do dome serious battlefield control by having the whole battlefield haunted in your favor.
I have been rather busy lately so I don't know what the current consensus is about the spiritualist class as of now, but it seems to still be one recognized to have a lot of roleplaying potential. I myself like the idea of ghostly companions and made a lot of characters with ghost familiars or companions but like it that if a character has a single ghost contact would also extend influence and interaction to other undeparted souls wandering around finding something to do.