Here's why:
* "To be" is the infinitive form of the verb "be".
* Verb phrases consist of a verb and any auxiliary verbs (helping verbs) that modify it.
* In this case, "to" is the auxiliary verb (often called a "helping verb") and "be" is the main verb.
Therefore, "to be" acts as a single unit to express the verb's meaning, making it a verb phrase.