Final answer:
The author used the phrase "the enormity of the space around him and the loneliness of its silence" in the sentence to help the reader feel the boy's loneliness or exhaustion.
Step-by-step explanation:
The phrase from the sentence that the author used to help you feel the boy's loneliness or his exhaustion is "the enormity of the space around him and the loneliness of its silence." This phrase emphasizes the boy's isolation and the vastness of the landscape, creating a sense of loneliness and exhaustion. The author uses vivid descriptions of the landscape and the boy's reaction to it to convey his emotions.