Phoon is playful and energetic, hopping around and being happy after being activated while taking in her surroundings. However, she also enjoys causing destruction, as she proves to be conniving and laughs evilly as she destroys things, showing a malicious side.
When Jumba accidentally mutates her with his Plasmatic Englobulatron, she is aggressive and mean while she continues to destroy things. She hates it when people try to stop her and will harm anyone who tries to. However, she enjoys being rocked and hearing lullabies, which soothe her and put her to sleep, as well as reverts her to her normal size. After being reformed, she decides to use her powers on a lighter level for people to enjoy her wind for windsurfing. However, she will use her powers to defend herself when need be, such as during the battle against the Leroys.
Experiment 540 was the 540th genetic experiment created by Jumba with Hämsterviel's funding. She was designed to create devastating, typhoon-like winds. 540 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai, with 540's pod landing on a rooftop weather vane.
A breeze caused 540's pod to fall off the weather vane into the roof's rain gutter and roll down into a rain barrel, activating the experiment. 540 then proceeded to destroy the house.
Shortly after, 540 blew down some palm trees near Gantu's ship. When Gantu went out to try and catch 540, the latter blew a tree onto Gantu's head. The resulting concussion left him confused and disoriented, though he resumed searching for 540 anyway.
Meanwhile, Lilo decided to temporarily quit experiment hunting after an unfortunate mishap. She then attended Hip Hop Fusion, where she impressed some rich hippie girls by telling falsehoods about her life.
When Gantu later showed up at the school, thinking Lilo was hiding the experiment from him, Lilo tried to cover up the situation by telling the hippie girls that Gantu was her eccentric uncle Chester who wasn't quite right in the head. Due to his concussion caused by the blow he took earlier, Gantu believed the lies that Lilo told the hippie girls, and ended up thinking that aliens were only figments of his imagination. He then decided to go surfing at the beach.
Shortly after, Stitch (dubbed Wenceslaus by Lilo) arrived and attempted to tell Lilo about the rampaging 540. The hippie girls initially questioned Stitch's body language, but then assumed he was an exotic pet. Unfazed by their opinion, Stitch tagged along with Lilo and the hippie girls.
Later, Jumba and Pleakley tracked 540 down. Jumba then tested his latest invention, the Plasmatic Englobulatron, in hopes of catching 540, despite Pleakley's objection to this. Instead, the ray mutated her into a gigantic monster (as stated by Jumba: "76.3% chance will instantly capture experiment, 23.5% chance will destroy entire planet with big boom. This was other 0.2% chance."). After blowing down Jumba and Pleakley, 540 resumed her rampage.
Meanwhile, a delusional Gantu was shredding waves, while Experiment 625 tried telling Gantu that if he didn't catch 540, Hämsterviel would be furious. However, Gantu ignored Reuben, believing the latter and Hämsterviel were merely figments of his imagination. Reuben later called Hämsterviel, who advised the former to kick Gantu in the rear. In doing so, Gantu snapped out of his delusion, came to terms with himself, and set off in search of 540.
Sometime later, 540 arrived at Hip Hop Fusion Studio and wreaked havoc with her devastating blasts of wind. She was soon followed by Gantu, and later Jumba and Pleakley. When the hippie girls grew suspicious, Lilo was forced to lie to them even more.
The mutated 540 destroyed a large portion of Kokaua Town until Stitch arrived and, after a long battle, succeeded in putting 540 to sleep by rocking her while singing a lullaby. This caused the Plasmatic Englobulatron effect to wear off, and 540 shrunk down to her normal size. When Gantu then attempted to capture 540 in a container, Stitch drooled menacingly, forcing Gantu to surrender.
540, christened Phoon, later found her one true place providing adequate winds for windsurfers.
The first 624 experiments, including Phoon, were round up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu arrived before the experiments could be destroyed.
Phoon participated in the following battle between the experiments and the Leroy clones by creating cyclones that sucked up Leroys and hurled them through the air.
However, the Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben and several other experiments performed the song "Aloha ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
Phoon made an appearance in the Stitch! anime where the gang went back in time and tampered with Stitch's creation, which started up his glitch and therefore almost erased him from existence. Phoon, along with Ace and Sparky, helped gather enough energy to re-energize Stitch.
- Phoon resembles an Octorok from The Legend of Zelda series or a Fiery Blowhog from the Pikmin series.
- Phoon's wind blasts are actually recycled sounds of Hathi, Jr.'s trumpeting from The Jungle Book.
- Phoon is one of the rare experiments to have green eyes instead of black ones like most of the rest.
- Phoon's pod color is blue.
- Phoon is described by the experiment computer screen as, "Experiment 540. Primary function: Creates typhoons."
- In Leroy & Stitch, both Phoon's mutated and normal forms appeared, possibly indicating that she has learned to morph in between the forms.