The invention concerns a method for producing phosphoric acid, which consists in: at least an attack of phosphate ore with an attacking liquid containing soluble phosphate ions, forming of an attacking product, separating in the attacking product between an insoluble solid phase containing impurities and a liquid phase having soluble phosphate ions and calcium ions, introducing in the separated liquid phase an acid stronger than phosphoric acid and which forms, with said calcium ions, a soluble calcium salt, and isolating a solution of said calcium salt, not contaminated by the impurities, thereby obtaining a phosphoric acid solution.