In which sentence is the underlined phrase an adverb phrase?

The students called several of Mr. Bruns’s former students.

The students gave Mr. Bruns a book of his favorite verses.

The students in Mr. Bruns’s class planned a party for his retirement.

Mr. Bruns had been teaching for 35 years.

The students called several of Mr. Bruns’s former students.

Explanation: In this sentence, the underlined phrase "several of Mr. Bruns's former students" modifies the verb "called" and functions as an adverb phrase.