Definitions

1. adjective

extremely phlegmatic; characterized by or having a high level of phlegm or apathy

“She described her aunt as the phlegmiest person she’d ever met, who never showed any emotions.”

2. superlative form of adjective ‘phlegmatic’

most phlegmatic; having the highest level of apathy or lack of emotion

“After the breakup, he became the phlegmiest person in the group, barely reacting to the news.”