Question

is the group of words in bold a phrase or a clause?
usually the result of earthquakes or volcanic activity, tsunamis are enormous ocean waves that can devastate docked ships; meanwhile, ships at sea may not even detect the massive waves.
phrase clause

Explanation:

A clause has a subject and a predicate. "Tsunamis are enormous ocean waves" has the subject "tsunamis" and the predicate "are enormous ocean waves". A phrase lacks a subject - predicate relationship.

Answer:

clause