Don't get infinitive phrases mixed up with prepositional phrases.
Prepositional phrases include to + a noun.
Infinitive phrases include to + a verb.
Anna went to the mall to buy a dress for homecoming.
Prepositional Phrase: to the mall is the prepositional
Infinitive Phrase: to buy is
the infinitive phrase.
Here are some sentences for you to practice diagramming infinitives:
1. Lisa loves to swim.
2. This is the bus to take.
3. To mow the lawn is my summer job.
4. To give is to receive. (Hint: You'll need 2 steps)
5. We watched Tim score in his game.