It's not. It's musical theatre, not true opera. The lines are blurred somewhat, but the major differences are: musicals have a greater emphasis on dance and acting whereas in opera, the emphasis is on the singing (a major opera star is not necessarily an actor); musicals incorporate popular and commercial music styles, generally sung in a style that would not be appropriate for opera; a greater proportion of the libretto for the musical will be spoken dialogue rather than sung. And a few other things.
Very little of the dialogue in The Phantom of the Opera is spoken rather than sung. The same is true of Les Miserables. They're what's known as sung-through musicals.
When I went on a cruise on Royal Carribean, we went to their Broadway production of "CATS". We liked it so much that we went twice and then, once off of the ship and back in Atlanta, we went a third time to The Fox Theater on Peachtree St. We loved it.
HowEVER, most people tend to not like it. I'm a member of a Royal Carribean message board and there were so many comments about
how they couldn't stand CATS and didn't stay for the second half. And I remember when we were on board, I remember seeing empty seats the second half.
The reason they gave was that they didn't understand what was going on. They didn't understand the plot. And this play was in English. But it was SUNG - not spoken.
"CATS" was musical theater, not opera. Like Ransom said, alot of the emphasis was on dance. Here is a short clip emphasising that.
And just for spits and giggles, here is a clip of its most famous song, which you may recognize:
On the other hand, opera does not emphasize dance or popular people of the time. It's about the voice. While they do have sets and costumes, the voice is emphasized. And it being in another language, I can certainly understand why, not knowing WHAT was being sung, one might not care for it. Here's a song you may recognize:
Opera does not depend on a certain race or beauty or frill but, on the gorgeous voice and may this diva rest in peace: Jessye Norman