Does Cute Poison actually work?
The Wikipedia page on "Cute Poison" episode says that it wasn't anhydrous copper (II) phosphate, but Gypsum.

I haven't seen the episode, and the Wikipedia page's reaction seems to be the backwards reaction of yours. But I imagine yours is the one the pro/antagonist is gonna use to escape the prison; as


Gypsum is commonly found and accessible:


  Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula $\ce{CaSO4·2H2O}$. It can be used as a fertilizer, is the main constituent in many forms of plaster and in blackboard chalk, and is widely mined. A massive fine-grained white or lightly tinted variety of gypsum, called alabaster, has been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, Byzantine empire and the Nottingham alabasters of medieval England.

Calcium phosphate's solubility will decrease with temperature increase and it will precipitate, leaving you with a solution of sulfuric acid.


It's possible for a double displacement reaction to occur in aqueous medium (with a spark):
$$\ce{2H3PO4(aq) + 3CaSO4(aq)·2H2O(l) \leftrightharpoons 3H2SO4(aq) + Ca3(PO4)2(aq) + 6H2O(l)}$$

$\ce{H2SO4}$ is sulfuric acid. It's a very strong acid in water, a diprotic acid. Its $p {\rm K_a}$s are −3 and 1.99 according to Wikipedia.


  Its corrosiveness on other materials, like metals, living tissues or even stones, can be mainly ascribed to its strong acidic nature and, if concentrated, strong dehydrating and oxidizing properties.


Later in the same article, you can read how it reacts with different material. It can weaken metal pretty fast and easily, as 3 moles of it will be present in any 7 moles of products, which is high above the dilute concentration (arbitrarily) defined in the Wikipedia page.

Copper sulfate also reacts with phosphoric acid and forms sulfuric acid, but it's hardly accessible in prison, I reckon.