Phish.com says the following: "This was Phish’s first known show in Worcester. The show was not listed in the December 1989 or January/February 1990 Phish Updates. According to Trey’s notes the band performed from 10pm – 1am. The show took place during a snow storm and was sparsely attended. The setlist is unknown."

However, I just talked to one of the people who booked the show - he remembers it being packed, as do I! Also, he remembers that they used the trampolines - he thought they were going to go through the roof! I don't have a definite memory of that, but if it is true, then it may be the earliest recorded example? The FAQ here gives 3/10/90 as the earliest known date (not sure why)