Conversation so far:
when did phantom of the opera debut on broadway
The 1986 musical The Phantom of the Opera opened on Broadway in 1988.
who wrote the music for the 1986 musical the phantom of the opera
The 1986 musical The Phantom of the Opera is a musical with music by Andrew Lloyd Webber.
who wrote the lyrics for the 1986 musical the phantom of the opera
Richard Stilgoe wrote most of the original lyrics for the 1986 musical The Phantom of the Opera. Charles Hart later rewrote many of the lyrics.

Question: what is the musical based on
Self-contained rewrite: what is the 1986 musical the phantom of the opera based on