Identify the adverbial phrase in the following sentence.

Saturn's most famous feature is its ring system that is made mostly of ice particles.

most famous feature

its ring system

of ice particles

that is made

The answer is: most famous feature.

An adverbial phrase can contain one or more words which function as an adverb, being the adverb the head word of the phrase. Thus, they modify an adjective, a verb or another adverb. In the example sentence, the word most is the adverb, which means to the greatest extent.

The phrase "its ring system" is a noun phrase, "of ice particles" is a prepositional phrase, and "that is made" is a defining relative clause.