The prepositional phrase 'about the main conflict' in the given sentence modifies the verb 'write', indicating the subject Julia will write about.
The prepositional phrase "about the main conflict" in the sentence 'When her English teacher gave the essay assignment, Julia knew she would write about the main conflict' modifies the verb 'write.' Prepositional phrases act as modifiers, offering details related to the action of the sentence. Here, the phrase specifies the focus or subject matter of Julia's writing, giving context to the action of writing. It answers the question "What will Julia write about?" and provides additional information about the content of her essay. Prepositional phrases play a crucial role in conveying specific details and nuances within a sentence, enriching the overall meaning and helping readers understand the relationships between different elements of the sentence.