Phoebe Waller-Bridge's uncouth one-woman show is seen as the epitome of festival success. But 10 years on, we speak to three fringe performers battling to escape its long shadow Ten years ago, Phoebe Waller-Bridge perched on a stool and delivered a line about having a massive arsehole in a manner that was precision-engineered to make the audience gasp and laugh. It worked on me. It clearly worked for other people, to…