Lily Tomlin’s performance Thursday night of “In Search for Signs of Intelligent Life in the Universe” at the Booth Theatre on Broadway really brought the house down, but it was Act II that had a real ring to it. In the middle of one of Tomlin’s intense monologues by her character “Trudy,” an extremely philosophical homeless woman who communicates with aliens, an audience member’s cell phone rang — twice. At first the stunned audience seemed confused as to whether the ringing was part of the show. Tomlin was confused as well and stopped to ask the offstage house manager where the noise was coming from. “In the house,” he replied — which set Lily off into a tizzy. “I know you think this is part of the show, but it’s not,” she said, before proceeding to playfully threaten to come out into the audience and find the cell phone-carrying offender. “In Search for Signs of Intelligent Life in the Universe” marks Tomlin’s return to the Broadway stage since the play’s original run in 1985, which earned her a Tony Award for Best Actress in a play.