How does each of the three phases of gastric secretion promote and facilitate gastric control?

Food entering the stomach will first pass through the:

Proton Pump Inhibitors (or PPIs) are some of the widely used drugs in the world and are prescribed for chronic heartburn/acid reflux. They work by inhibiting the movement of H⁺ ions across the membrane into the gastric juice, thereby lowering the concentration of HCl. As described, which cell of the gastric glands would you expect PPIs to affect?