Andrew is not an attorney, and I don't necessarily expect precision from him when discussing legal matters. (I don't expect it from Prosper's attorneys either, but that's another matter.)
Perhaps he meant to type "phone number," or perhaps he meant the attorney's internal "file number."
I don't know how quickly PACER is updated once a BK is filed, but I suspect that it is rather quick, and it's certainly a painless way to ascertain whether a BK has been filed.