Well, drying agent is the most important use basically, it is used alot in desiccators, being the strongest agent for this purpose, except maybe conc. sulfuric acid. I read of it being used to heat trekking meals, because it reacts so extremely exothermic with water (do watch out! it must be added to water, not other way round), that's a pretty cool explanation, ain't it? It is also important to make esters of phosphoric acid, these are for harmless organic chemistry (Michaelis-Arzhubov-Reaction, makes alkenes - tributyl phosphate is also used to extract thorium, uranium, so avoid that one). Hope this helps. Also as mentioned before it is used to make polyphosphoric acids. But really, I think this one isn't watched.