Specifically, to put an end to it. Extra specifically, if you had something important to it in life, such as a prized possession, or especially its own mortal remains.
I admit, I love watching me some Supernatural, and this sort of thing seems to come up a lot. So I thought about it, looked at spells like Speak With Dead, Planar Binding, Ghostbane Dirge, the 3.5 spells Make Manifest and Ghost Trap, and the glorious Incantations from 3.5 Unearthed Arcana. And really, I think its just fine that there might be a way to do such a thing. And especially likely that the church of Pharasma would know how.
Still, while I will run my home games the way I want to run them, I want to know how the rest of you feel regarding the subject. Note "subject" rather than "mechanic". This isn't a rules question so much as a "spirit of the game" question. Although I suppose it is also a bit "setting" related too. I'll understand if this thread gets moved.
So, what do you all think? Could a knowledgeable person summon a spectre/shadow/wraith if they dug up it's bones and enacted a proper ritual?
I think that a rite to "summon" a specific entity by using its mortal remains could certainly work. I'd probably throw in a requirement for knowledge of its name, as well (or at least a bonus on the save if the caster didn't know it).
I put quotes around summon since what you want is an actual presence, and summon spells just make cheap copies.
You'd want a containment circle, like for the Planar Binding spells -- oh, hey; Planar Binding has a decent mechanic for what you want, just shifted from an entirely other-planar being to a half-other-planar one.
So, the above is rather mechanic-oriented. So let me say that I don't see any glaring issues thematically with the concept. Hence, my diving into "how to do it," since I think the doing would be fine.
Couldn't use spell research mechanics to make up such a spell, not unlike other summoning spells?
Pretty much what Aitan said: yes, I think it works with the spirit of the game, and mechanically planar binding is a great place to start (with special variants of the "magic circle" spells for undead, too).
While the church of Pharasma might know such rites, I'd suggest that the churches of Sarenrae, Nethys, Urgathoa, and Norgberger would likely know them as well, though each for very different reasons from each other and Pharasma (except maybe Sarenrae: I'd imagine her and Pharasma's churches get on well considering how they both feel about undead).
Keep in mind, however, planar binding (and variants) are very powerful spells, and they require great effort to achieve. They'd tend to be quite rare and difficult, over all.