Here's why:
* Verbal Phrase: A verbal phrase is a group of words that includes a verb form (a verb that acts as another part of speech) and any modifiers or objects.
* Infinitive: An infinitive is the base form of a verb preceded by "to" (e.g., "to run", "to eat", "to sleep").
* Infinitive Phrase: An infinitive phrase is an infinitive plus any modifiers or objects that function as part of the phrase (e.g., "to run a marathon", "to eat a delicious meal", "to sleep soundly").
In short, because an infinitive phrase contains a verb form (the infinitive), it is classified as a verbal phrase.