Final answer:
Phil, the subject of the sentence, opened a book authored by Charles Dickens, indicating the subject is related to literature, specifically English literature. This topic is typically studied in high school English classes, where students analyze such books for their literary and historical significance.
Step-by-step explanation:
The subject of the sentence 'Phil opened the book given to her on her birthday by Charles Dickens.' is Phil.
This sentence is dealing with literature, specifically noting an action related to a book authored by Charles Dickens, a prominent British novelist. The subject is engaging with literary material, which can encompass aspects related to English language arts, reading comprehension, and textual analysis.
Given that Charles Dickens's works are often studied in high school as part of the English curriculum, the grade level is likely high school.
The use of Charles Dickens's books in the sentence also implies a connection to 19th-century literature, which is a common topic within English classes at the high school level. Additionally, knowing the historical and cultural context of Dickens's work can enhance understanding, tying in elements of social studies and history.