Can you help me think of an idea for my level 3 question about Phantom of the Opera?

A Level 3 question moves beyond the text itself and facts about the text to ask what sort of implications the text has or what sort of challenges it offers to broader systems of ideas. Such a question often has a moral dimension, asking what the text says about issues not just of how characters lived their lives but also about how characters (and real people) should live.
I find the most problematic aspect of the novel the way it handles disability. The romantic figures of Christine and Raoul are traditionally young and attractive. They are portrayed as morally good figures who fall in love and are rewarded, after various perils and obstacles, with a happy marriage.
Erik, however, is a more problematic character. His disfigurement is a form of disability. Erik is the lover who helps Christine improve her singing and is intelligent and creative. We might ask why he is eventually made over into a villain by the plot. Although thematically the novel examines the nature of illusion, it still associates physical ugliness with evil. Even Erik's partial redemption at the end of the story is due to his love for a young beautiful woman.
You might want to examine how the novel itself and its being taught in schools reinforces prejudices against the disabled and encourages an attitude that correlates physical attractiveness with moral character.
Another question you could examine is the trope of woman as reward. Thus you could think about the degree to which Christine is a reward in a contest between Erik and Raoul versus the degree to which she is portrayed as an independent person who makes active choices.

Level 3 questions are generally thought-based questions that ask the reader to draw the material together thematically (as opposed to level 1, or fact-based questions, and level 2, or inference-based questions). Some questions you might consider are the following:
How does Erik represent Christine's darker, more evil self? How does he embody her deepest dreams and desires?
What is the religious symbolism of Christine (a Christ-like figure, as her name implies, who redeems the Phantom) and of Erik (a dark figure of the underworld)? What are the book's larger religious messages?
In The Phantom of the Opera, the company is producing Faust. How is Faust similar thematically to what is happening in The Phantom of the Opera? Which character in Phantom is most like Faust?
How does the author humanize the figure of Erik in the end?
What does Christine's vacillation between Raoul and Erik symbolize, and what does it suggest about her character and desires?