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 contains a subject and a predicate (a verb that shows action or state of being). The bolded text "tsunamis are enormous ocean waves that can devastate docked ships" has a subject ("tsunamis") and a predicate ("are enormous ocean waves that can devastate docked ships") which includes a linking verb and descriptive/action elements. A phrase lacks a subject-predicate pair, so this is a clause.

Answer:

clause