**Core Concept**
The gastric secretory process is a complex physiological response that involves the coordinated action of various neural and humoral mechanisms to facilitate digestion. The stomach secretes digestive enzymes and acids in response to the presence of food, and this process is divided into three main phases: cephalic, gastric, and intestinal.

**Why the Correct Answer is Right**
The gastric phase is the period during which the stomach secretes the greatest volume of gastric juice, which is rich in hydrochloric acid (HCl), pepsinogen, and mucus. This phase is triggered by the arrival of food in the stomach and is characterized by the release of gastrin, a hormone produced by G cells in the antrum of the stomach. Gastrin stimulates the parietal cells in the gastric glands to secrete HCl, which creates an acidic environment that activates pepsinogen to pepsin, a digestive enzyme that breaks down proteins. The gastric phase is responsible for the majority of gastric secretion, with the stomach secreting up to 2 liters of gastric juice per day.

**Why Each Wrong Option is Incorrect**
**Option A:** The cephalic phase is the initial phase of gastric secretion, which is triggered by the sight, smell, or thought of food. While it does stimulate gastric secretion, it is not the phase during which the greatest volume of gastric secretion occurs.

**Option C:** The intestinal phase is the final phase of gastric secretion, which is triggered by the presence of partially digested food in the small intestine. During this phase, the stomach secretes a small amount of gastric juice that is rich in bicarbonate, which helps to neutralize the acidic environment created by the gastric phase.

**Option D:** Deglutition, or swallowing, is the act of propelling food from the mouth to the stomach. While it does stimulate gastric secretion, it is not a phase of gastric secretion in and of itself.

**Clinical Pearl / High-Yield Fact**
The gastric phase is also known as the "gastric mill" phase, during which the stomach secretes a large amount of gastric juice that is rich in digestive enzymes and acids. This phase is critical for protein digestion and is often impaired in patients with peptic ulcer disease or gastric cancer.

**✓ Correct Answer: B. Gastric phase**