Phlegmatic
adjective

1. Referring to or characterized by phlegm, a clear, viscous bodily fluid secreted by the mucous membranes of the respiratory passages as a response to irritation or inflammation.

2. Having a calm, unemotional, and unexcitable temperament.

3. Displaying a sluggish or apathetic disposition.

Phlegmatic (noun)
noun
A person who possesses a phlegmatic temperament, typically identified by their calm and unemotional nature.