It could, it is often a reason that people will add sand to begin with. It is why people use phosphate reactors in BB systems. I'm not sure about its effects on denitryfication. If your levels of phosphate were high enough to effect this process than you would already be in deep trouble
This is why the bucket idea is so nice, it is very simple to just replace the bucket with a new one with new sand, all new substrate for phosphate to bind to.