@ledzepmaster said:

It's not a teleprompter, it's a song bank.

What's a "song bank"?

According to the Phish.net FAQmany believe it's a teleprompter device designed for live music (unlike the typical double podium mirror style used by public speakers like Presidents for decades) known as a "Wolfgang telemonitor", which looks from the front of house like a wedge monitor and is believed to display both setlists and lyrics of new/rare songs from the rotation, and in the latter instance, the scrolling speed, can be controlled by a foot pedal.

(And, as Jerry Seinfeld said, not that there's anything wrong with that, remembering all the lyrics of several hundred songs is very difficult and sometimes a lead singer needs a crutch just in case).