PTH causes increase in the blood Ca²⁺ levels by contributing to an increase of all the following processes, except

PTH acts on the kidneys to promote formation of the hormone calcitriol, the active form of vitamin D. Calcitriol increases the rate of Ca²⁺, HPO₄ ²⁻, and Mg²⁺ absorption from the gastrointestinal tract into the blood.

Parathyroid hormone (PTH) is a hypercalcemic hormone which increases the Ca²⁺ levels in the blood. 

PTH stimulates bone resorption (dissolution/ demineralisation), reabsorption of Ca²⁺ by the renal tubules and increases Ca²⁺ absorption from the digested food.