Here are a few for starters:
The cript of Christine's father is a symbol--the family name is DAAE pronounced "die" and she undoubtedly thinks of death as a friend having been orphaned and tormented with internal and external conflicts through the opera, her musical training, and her purpose in life.
The Opera itself is a symbol. It symbolizes sanctuary for all the orphans and escapees--the phantom, Christine, other dancers and actors without any other place to go.
The mask the phantom wears is a symbol. It is is safe-haven outside of the catacombs of the opera. His way of hiding the hideously deformed face from society--his beautiful face to go with the beauty of his musical talent.
Music is a symbol--it is the hope and life-giving blood of so many, but especially the phantom and Christine. The phantom's voice has come to Christine in many hours of need. She has clung to it as her father told her on his deathbed that he would send her the Angel of Music to look after her in his absence. Music is the connection between the phantom and Christine, and the phantom has trained her secretly for years developing her lovely voice.
I have an entire blog and also a book dedicated to the symbols in the Phantom of the Opera. It takes a look at the characters, emotions, and sets. The Phantom of the Opera is a chilling tale interlaced with darkness, despair, love, and redemption. Originally penned by Gaston Leroux, the book is classic literature. Leroux weaves the tale of a deformed man living in isolation underneath the Paris Opera House, who desperately loves a beautiful girl named Christine Daaé. The masked man has many names - Phantom of the Opera, Opera Ghost, Angel of Music, and Erik. He is a broken soul who yearns for beauty, but lives in hell. His desperate search for love takes him down a road of obsession and violence, and the cry of his despair echoes in our hearts. “All I wanted was to be loved for myself." Lessons from “The Phantom of the Opera” steps behind the scenes and examines the symbolism hidden in the characters, emotions, sets, and events. The book leads its readers on an emotional journey studying the motivations of the characters and the numerous symbols hidden throughout the Opera House. It examines not only Leroux’s original work, but also analyzes the play and movie. Personal reflection is encouraged, and the author poses questions to incite further thought and revelation. As a result, lessons and life applications emerge from a timeless masterpiece for everyone to enjoy.