Demon's Souls boss drop

So I beat the phaleynx or however you spell his stupid name and he dropped a rare item the phaleynx soul, should I use it or save it for someone.

What do I get if I use it.

You can use it to get the scraping Spear which if you have a Spear +7 and that Phalanx Soul you get the Scraping spear but its best use is PvP.

So I just use the item and get his weapon? or it combines with a spear I purchase?

So bottom line is just use the item right and not save it...?