Question

is the group of words in bold a phrase or a clause?
gongs, circular metal percussion instruments, originated in china, where they were—and sometimes still are—used in ceremonial events.

Explanation:

A phrase is a group of words without a subject - verb relationship, while a clause has a subject and a verb. The bolded group "circular metal percussion instruments" has no subject - verb combination (it's a noun phrase with modifiers), so it's a phrase.

Answer:

The group of words in bold ("circular metal percussion instruments") is a phrase.