Joey and Rachel spend time engaged.
Ursula dies.
Mysterious man appears wanting Phoebe to go away with him. Phoebe is very upset and won't go "at least not yet". Monica over hears this and wants to know what the deal is but Phoebe won't discuss it. We later learn that the man was her supervisor at the think tank she worked for. It turns out that Phoebe is a super-genius and they want her to come back now that Ursula is gone. She left because Ursula is just ordinary and she was putting Phoebe down and Phoebe sort of snapped and spent years trying to prove that she was just as good as Ursula; a typically confusing story. They really need her back to work on the super secret project she was last working on (Project Smelly Cat). But she won't go because she has one last piece of unfinished business.
Joey has a birthday and his career dies -- he's too old.
Phoebe's last bit of unfinished business is Joey; she's in love with him and she isn't leaving without her man.
Ross marries Rachel and Joey marries Phoebe in a double ceremony. Joey and Phoebe move off to secret facility in Nevada.