Final answer:
The infinitive phrase in the sentence is 'to grab a snack,' serving as an adverb that modifies the verb phrase 'she went home' by showing the purpose of the action.
Step-by-step explanation:
The infinitive phrase in the sentence “She went home to grab a snack out of the fridge” is to grab a snack. An infinitive phrase usually begins with the word “to” followed by a simple verb form. Infinitive phrases can function as nouns, adjectives, or adverbs within a sentence.
In this case, the phrase is functioning as an adverb, modifying the verb phrase “she went home” by indicating the purpose of going home.