Answer:
The infinitive phrase is "to watch two movies in a row"
Step-by-step explanation:
An infinitive phrase is one that has the verb in the infinitive mode, in addition this phrase may have elements modifying and complementary. Infinitive is a verbal form where the verb is usually after the word "to". Thus it is easy to perceive the infinitive phrase of the question, since the verb "watch" comes after the word "to".