Twenty years ago or more, Phoenix Theatre operated a black box, where those of us who liked edgier plays and musicals could go for offbeat theater. Late last year, the now-93-year-old company unveiled, as part of its multimillion-dollar renovation, a new black box space. Those of us who once laughed ourselves silly over campy Charles Busch comedies are older now and want more from our offbeat theater — and we got it with this neat, comfortable black box space, where the company has offered smart, first-rate productions like Ruthless! The Musical and Avenue Q.