Make sure you do research to see what audiences want, like and expect nowadays, whether it's on telly, YouTube, Netflix or live.

A lot of it is in delivery and performance, so I don't mean this to sound harsh as I've only seen it written down, but the punchline of that story probably isn't enough of a surprise to cut it on stage, even if it slays people down the pub. If you stopped people halfway through and asked them to guess the ending, I bet most would say "the phone hadn't really been stolen"

EDIT: having said that, the point of the course is to make your material good enough for performance on stage, I guess.