Phar-Mor was a discount drugstore, though perhaps it would be more accurate to say that it was a mini-department store (think Walgreens, but larger) that filled perscriptions. This store on Harbison, next to the Barnes & Noble, is the only one I'm aware of in Columbia (I also know of one that was in Aiken at Aiken Mall). At one time, the Phar-Mor chain appeared to be a category beater, growing faster and bringing in more money than any of its competitors. Unfortunately in the aftermath it emerged that the whole thing was a giant crooked pyramid scheme with the founder cooking the books right and left. The chain went into bankruptcy, and the founder went to jail. I believe the chain struggled on a while after this store closed, but finally went totally under in 2002.
Ross Dress For Less has occupied the spot since Phar-Mor closed, and seems to be doing well. The strip mall seems to have regular turnover of smaller storefronts, but luckily has been able to hold on to (or in this case replace) the anchors.
UPDATE 26 Sep 2010: I've added the full address to the post title. However, while the current address appears to be 287 Harbison Boulevard, my older sources give the address as 272 Harbison Boulevard, so apparently there has been some re-numbering within that plaza.
UPDATE 20 March 2011: Updated the closing date based commenter Andrew's research, also added the store number "0229".