When the curtain is held for 15 minutes and the director steps on stage to apologise for the virus that has afflicted the star and others in the company, a first-night audience is entitled to be apprehensive. It need not have worried.     Anthony Warlow and the splendid cast assembled for this revival, on the same stage first stalked by Warlow's Phantom 17 years ago, certainly "gave it a go", as director Arthur Masella promised they would.     Warlow had a slight dropout on one sustained note and opted for one alternative note, but otherwise there was no cause for disappointment.  His exquisite falsetto in The Music of the Night was as enthralling as ever, and his strength and power when the Phantom gives vent to anger and passion was as majestic.     Warlow plays the Gothic romantic melodrama to the hilt as the disfigured composer who lurks in the bowels of the Paris Opera House.     Svengali-like, he champions the career of young singer Christine Daaé, with whom, Beauty and the Beast-like, he falls in love.     Phantom is a show for good singing, and Warlow is wonderfully supported by gifted coloratura Ana Marina, dainty and vivacious as Christine, and John Bowles, who acts and sings the role of Raoul, Christine's childhood friend and suitor, with buckets of charm.     The vocal work of these three is a treat.     Good singing in a rarer discipline comes from Andrea Creighton and David Rogers-Smith, amusingly over the top as the opera's underwhelming stars, Madame Carlotta and Signor Piangi.     John O'May and Derek Taylor are excellent light relief as the new managers of the opera house, and Jackie Rees is a forbidding presence as the ballet mistress, Madame Giry.     Whatever its merits as words and music, The Phantom of the Opera is the most sumptuous theatrical spectacle.  When Harold Prince directed it in London back in 1986, he gave it the full treatment.     There was no stinting on scenery and costumes, so the customers could see how virtually every cent of their ticket money had been spent.     And it's good, old-fashioned backstage artistry -- not a computer graphic or projection in sight.