Here's why:
* Adverb: An adverb modifies (describes) a verb, adjective, or another adverb. It answers questions like "how," "when," "where," or "to what extent."
* Verb Phrase: A verb phrase consists of a main verb and one or more helping verbs. In this case, "run" is the main verb, and "slowly" is an adverb modifying the verb.
Therefore, "slowly" is the adverb in the phrase "run slowly".