I think I picked a couple up from some mod at some point maybe? I might be wrong, but I think there were a couple of bottles labeled White Phial in the upper residence from the Elvenwood mod.
Yeah, it's a bug--they're junk. I think getting rid of the empty ones makes the phial stop working.
I think it is a bug too, I play on the xbox 360, my play throughs have multiplied them, having one filled and the other used, also have had them multiply, then when try and remove them from the inventory and put them in a house or use them for decoration, I think I always found them missing just like one of the dragon priest masks that ends up missing if you drop it, but will stay in a chest or in the inventory