Julianna is Claire Dunphy]'s alter ego she created for her Valentine's Day dates with Phil's alter ego Clive Bixby, introduced in "My Funky Valentine". They usually appear together on Valentine's Day episodes throughout the series, expect in season 6, where Julianna met with and seduced Phil as himself and not Clive. In Bixby's Back, she describes herself as a "bored housewife with a dark side and an hour to kill."
In "My Funky Valentine", she gets "picked up" at a hotel bar by Clive, who is married but "respects her wife too much to do the things he's going to do to [Julianna]". She goes to the bathroom and returns wearing a coat and nothing underneath, inviting Clive upstairs. Things get an unexpected turn when her coat gets stuck on the escalator.
They meet again in Bixby's Back, after Claire decides she is not ready to give up the excitement with Phil. She gives him her hotel room key, but the distracted Clive accidentally grabs an old woman's key instead.
She briefly appears in Heart Broken on a date with Clive, though Claire slips in and out of character as she worries about the kids. Claire later suffers a minor arrhythmia and is taken to the hospital, cutting the date short.
In Valentine's Day 4: Twisted Sister, after Claire calls and cancels her date with Phil, Julianna appears and seduces him. Phil is enticed by her, stating she is "adventurous and surprising", making Claire think he's more in love with her alter ego. Claire later tries to sabotage Julianna's appeal to Phil by saying she has an infected toe, lives with no electricity, and hates Dirty Dancing.