Locate the complete infinitive phrase and identify its use.

Tom and Tim decided to spend the afternoon tobogganing.

The infinitive phrase is "to spend the afternoon tobogganing".

An infinitive phrase expresses the action in a sentence. They can often function as nouns, adjectives or adverbs. E. g.: To win the approval of her mother-in-law by cooking dinner was Mary's only hope. The infinitive phrase in bold functions as a noun because is the subject of the sentence. When the phrase explains 'how' it functions as and adjective, when the phrase explains 'why' it functions as an adverb.

infinitive phrase: to spend the afternoon tobogganing.

use: noun