ANTHONY Warlow is again the man in the mask. ANTHONY Warlow is again the man in the mask.     Last night, at the Princess Theatre, the golden voiced singer shook off the "virulent virus" that knocked him flat for a week and reclaimed the title role in The Phantom of the Opera .     Warlow, Australia's original Phantom in 1990-91, struggled through the gala first night, but understudy Simon Pryce covered seven performances after that.     During previews, Warlow seemed immune to the flu that felled other Phantom cast members.     But on the eve of opening night, he showed all the symptoms: aches, pains, and dizziness.  Doctors recommended rest and told Warlow his vocal chords were not damaged.     "I warmed up at home before the show and could sing the notes," he said.  But later, in his theatre dressing room, Warlow struggled to make any sound.     "It was terrible. When (producer) John Frost came in, I was almost in tears.  I felt I was letting the whole city down if I didn't go on."     Finally, about 6.30, Warlow told Frost he was not well enough.     Half an hour later, director Arthur Masella changed the singer's mind -- he proposed telling the audience some cast members were unwell but would do their best.     Pryce shadowed the ailing star for 2 1/2 hours and saw him doubled over.     Warlow admitted it was tough: "My voice was popping and squeaking but halfway through the boat scene, I thought: so be it.  In my deluded state, I decided to try and instil everything that was happening to me into the character."     After that, "the heat of the performance kicked in" and Warlow earned a standing ovation.     "Part of me wants to forget that night," he said.  "But I'm also proud that I got through it."