Which term is related to phlegm and describes an unemotional disposition?

The term "phlegmatic" is indeed related to phlegm and describes a person who is calm, reliable, and consistent, often displaying an unemotional and phlegm-like disposition. Historically, the concept of the four humors in ancient medicine associated phlegm with a temperament characterized by calmness and a lack of emotional response; thus, individuals with a phlegmatic temperament are often seen as composed and uninterested in strong emotional expressions.

This connection between the term and the description makes "phlegmatic" the most appropriate choice. In contrast, the other options point towards different meanings: "composed" emphasizes calmness but does not directly relate to the clinical or historical context of phlegm; "sentimental" indicates a strong emotional disposition; and "appeasing" suggests a tendency to placate others, which also diverts from the unemotional characteristic associated with the phlegmatic disposition.