Answer: The correct answer is : The phrase in the infinitive is: To do one's best
The theme is: The triumph is the final goal but the desired, the goal to achieve is "one's best".
Explanation: A phrase in the infinitive is one that has one or more verbs in infinitive mode. The infinitive is a non-personal verbal form since the verb has no mode, person, time or number. The infinitive is formed with "to" + basic form of the verb. In the case of the sentence of the question, it would be: To do