She is voiced by Chelsea Peretti.
In "Cellsea", Leah Birch got a new phone and gave her old one to Nick Birch, which was a good replacement for his old phone. The phone's name was Cellsea and she was confused when she was given to someone else. At first, Cellsea didn't like Nick but she very quickly grew attached to him and before long, the two became the best of friends, looking up funny stuff on the internet and recording funny situations.
In "Obsessed", Nick became obsessed with Cellsea to the point where he was always on his phone and never paying attention to the world around him, which got out of hand when Nick recorded Elliot Birch dancing naked in the bathroom, which got him in trouble with Diane Birch, who confiscated Cellsea. Nick later snuck into the air vents and broke Cellsea out of the confiscation box and played with her. Diane later came back and punished Nick for this by jamming a fire iron through Cellsea's screen, killing her and thus destroying Nick's new phone.
- The name Cellsea is a pun on Chelsea.
- Her voice actor's name is "Chelsea".