**Core Concept**
The esophageal phase of deglutition, also known as swallowing, is the final stage of the oral and pharyngeal phases, where food is propelled into the stomach through the esophagus. This process involves coordinated muscle contractions to ensure the bolus reaches the stomach without aspiration.

**Why the Correct Answer is Right**
The esophageal phase is primarily caused by peristalsis, a wave-like muscle contraction that moves the bolus through the esophagus. This peristalsis is initiated by the entry of the bolus into the esophagus and is mediated by the esophageal smooth muscle, which contracts in a coordinated manner to propel the bolus towards the stomach. The lower esophageal sphincter (LES) also plays a crucial role in this process by relaxing to allow the bolus to pass into the stomach.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not relate to the esophageal phase of deglutition. The oral phase involves manipulation and mixing of food with saliva, while the pharyngeal phase involves the passage of food through the pharynx.

**Option B:** This option is incorrect as it refers to the relaxation of the upper esophageal sphincter (UES), which is not directly responsible for the esophageal phase of deglutition. The UES relaxes to allow the bolus to pass into the esophagus but does not propel it through the esophagus.

**Option C:** This option is incorrect as it refers to the gastric phase of digestion, which occurs after the food has entered the stomach. The gastric phase involves the breakdown of food by gastric enzymes and acid.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the esophageal phase of deglutition is a highly coordinated process, and any disruption in this process can lead to swallowing disorders such as dysphagia.

**Correct Answer: C. Peristalsis. Esophageal phase of deglutition is caused by peristalsis.