That Phineas & Ferb had such an odd reference that most of it's target audience won't understand it. It's the episode called the Lake Nose Monster. The lifeguard has gone into the sea after eating saying that the whole waiting 20 minutes was to sell "i've got a cramp" snowglobes. He ends up getting a cramp as Phineas & Ferb's boat, Nosebud, comes speeding towards him. Just before being saved by Candance from being hit by the boat, he whispers "Nosebud" and drops the snowglobe into the ocean.
If you didn't know, the reference is to a movie called Citzen Kane, made in 1941. At the beginning of the movie, a very wealthy man who lost his power and loved ones dies in bed holding a snowglobe. His last word was "Rosebud" and he drops the snowglobe on the floor where it smashes. In the end, Rosebud was the name of a sled he had in his childhood before he was taken from his parents and gained his wealth.
If you want, an episode of the Simpsons with the same name parodied the movie with Mr. Burns looking for his lost teddy bear Bobo.