The piece of paper is the business card of the vacuum repairman. "Hoover Max Extract Pressure-Pro, model sixty" is not a phone number, it's the passphrase to let the vacuum repairman know that you're looking to "disappear" — be extracted and have your identity changed.
Saul mentioned the passphrase the first time he called the vacuum repairman in S04E05 "Quite A Ride" (relevant part starts at 03:42):
Saul Goodman: I need a new dust filter for my Hoover Max Extract Pressure-Pro Model Sixty. Can you help me with that?
How hot? Red hot.
In El Camino, Jesse Pinkman tried to tell the passphrase to the vacuum repairman but does not have the exact passphrase memorized:
Jesse: Umm, I'm looking for a Hoover Max… Pressure Max. Max Pressure. Hoover, maybe it's a Pro Max. Hell, like a — like a filter?
Vacuum repairman: Hoover products are right over there at the wall behind you.
Jesse: Look, I don't remember the exact like password, alright but it's a vacuum thing.