I like opera singers, but have little experience in live Opera.
Is The Phantom opera?
I say it is.
I say it rocks my boat.
There is no simple answer to your question but it rocks your boat. It's a great joy in this hobby to find these personal treasures. Enjoy it however people decide to classify it.
I would not call The Phantom an opera. It's a musical (theater) that is very opera like but still it's a musical. Opera and musical are different in many different ways but there is one overriding difference that sort explains the rest of the differences. Opera evolved from music into theatrical music whereas musicals evolved from theater into a musical theater. A lot of operas can be taken in without the libretto being understood because the emotional impact is primarily delivered via music, both instrumental and vocal. Musicals on the other hand must have clear communication of the lyrical content because that is what drives the show. Can you appreciate a Shakespearean play that you can make out the lines the actors speak? Music just adds to what drama the lines contain. In other words, music is a secondary to the acting in musicals. In opera, it's the other way. Theatrics are secondary to the music in providing the drama.
Seen from this light, you can see why operatic singing is the way it is. The operatic singing uses the tonal output from the voice like an instrument in creating a dramatic art. The classical training elongates vowels to promote resonances above modal register to give singers rich output on higher notes. This type of singing can produce gorgeous tones but lousy diction. Sometimes subtitles are needed even when an opera is sung in English. Musical Theater singing however emphasizes clarity of diction. Everything must be sung like it's spoken. The singing techniques to keep vocal output consistent among registers are mostly thrown out and only the modal register (the speaking voice) is used to sing clearly. Modern belting techniques allow musical theater singers to produce loud, full and high notes that are clear in diction, albeit at a brighter and sharp tone. A lot of them though are not trained in this manner to fully engage the vocal chord and ancillary parts and depend on amplification to produce sound that will carry throughout the theater.
Andrew Lloyd Webber, despite accusations of "borrowing" music from others is a very talented composer whose popularity cannot be denied. He creates catchy, melodic tunes that stay with you. In Phantom of the Opera he employs through composition like opera and even uses the title song as a Leitmotive in the tradition of Wagner. I don't think Wagner would have approved Lloyd Webber though as he is much like Meyerbeer who was panned by Wagner. Much like the grand operas of Meyerbeer, Lloyd Webber uses grand scale in everything he does but lacks depth in thematic music structure to his composition. Let's call it a grand musical. The music alone will not carry the day without the theatrical narrative.
At the end of the day, it doesn't matter how we classify the Phantom. If you enjoy it and it rocks your boat then the producer of the show has reached you and that is all we are looking for from any music or play. And remember a lot of the critics are jealous of his success. Enjoy and give other more traditional Opera a chance in the future. Live Operas and musicals are so much better than recorded formats. I attend both all the time and enjoy them.