THE opera elephant is ready, the gargoyles are in position and no more run-throughs are needed for the "falling" chandelier.     All that remains now is for Anthony Warlow and Ana Marina to don masks and start performing The Phantom of the Opera.     "We've had such a successful rehearsal period," Warlow said yesterday at the Princess Theatre.  "Now, I'm just ready to go and do it."     Warlow has the title role in Andrew Lloyd-Webber's Gothic fantasia while Marina is the Phantom's beloved Christine.     On the eve of their first preview performance, both singers took Victoria's Tourism Minister Tim Holding on a backstage tour.     Warlow explained: "I once said Man of La Mancha was the King Lear of music theatre.  I think this is a very close second."     The Phantom opened at the Princess in December 1990 and toured Australia for seven years.     This production, opening July 28, leads a musical invasion of Melbourne: Priscilla, Queen of the Desert, Spamalot and Wicked bound for theatres in the next 12 months.     Warlow said Phantom's enduring appeal rested with its unabashed romanticism.  "It's beautiful to look at, wonderful to listen to, and you leave the theatre and can whistle a tune."