A solubility table may be something your class may want you to memorize. Where an aqueous (aq) solution is formed by a soluble compound dissolving in water, our solvent. So if we refer to this solubility table, it says phosphate (PO4) is usually insoluble, so in the reaction it won't break down in water and will stay as a solid (s). The only exceptions are group 1 alkali metals or ammonium (NH4+).
This is because it absorb heat from the surrounding which is required to break the bond hold it together hence as it absorb heat from the surrounding the temp of surrounding decrease.
