One of the show's running gags is that Phoebe has a huge and blatantly obvious crush on Coop Burtonburger. In several episodes in which she appears, she takes opportunities to get close and/or flirt with him. Coop, on the other hand, doesn't seem to return the affections, but on a few occasions, he does see her as a friend.
The following is a list of each of their interactions over the course of the series.
In the first intro, as Coop and Kat battle at the playground, she's seen waving at him.
When Coop answers the door, he encounters Phoebe in her Greenie Girls outfit selling cookies, who greets him in a smitten fashion. She also states that if she wins the bet between herself and Millie, she'll spend the afternoon with him. When Coop ultimately agrees to be in the bet, Phoebe is ecstatic and says she looks forward to it as she walks away. As Coop and Millie make their rounds selling cookies, Phoebe again greets Coop while jumping from behind a lamppost, and again gushes over her potential quality time with him. After Millie admits to eating her cookies (and thus losing the bet), Phoebe calls for Coop so that they can hang out, until he gets bailed out of it by Burt.
Among the people watching Coop's magic show is Phoebe, who's not only right up in the front away from everyone, but is also wearing a lavender sweater with his face on it. When he rejects Kat from the show and asks for a human volunteer, Phoebe immediately dashes up and endlessly says "Me!"
Phoebe smiles widely at Coop upon arriving at the house. She also tells him to come and watch her win seductively. When Coop first encounters Phoebe backstage, she tells him how happy she is that they're pet training together. While Phoebe applies a coat shine enhancer to Honey Fluff, she tells Coop that he's the only one she doesn't keep it a secret from with another seductive expression.
As the tour begins, Phoebe jumps to Coop and exclaims that she might need to hold onto his hand whilst hugging him. When the concrete chandelier falls towards Coop, Phoebe risks her life and pushes him out of the way, asking him if he's all right afterwards, and staring at him happily when he gets up. She appears to be the only other one (besides Dennis) to believe him when he discovers the traps are real, evidenced by her increased nervousness as the tour goes on. After Coop saves everyone from the walls of spikes, Phoebe calls him her hero and gives him a kiss on the cheek.
Phoebe states to Coop that she'll be his personal cheerleader during the game. She's then seen in the crowd with an "I Heart Coop" sign cheering for him.
Throughout the episode: first, she attempts to give Coop an invitation to her party since she considers him her extra special guest. When Coop is pushed by Kat in front of Phoebe and Burt (who were searching for him), she gleefully exclaims "There he is!" and runs to him. She tries to convince him again at Dennis's house, to no avail.
Each time Coop is teleported into Phoebe's house, she flirts with/shows affection to him. On the first time, she runs towards him to give him a hug, before holding his hands while saying "Oh, Coopie, I knew you couldn't stay away!" She then mentions how glad she is he came, then offers him cookies and a milkshake, calling him "Cooper Dooper" and "Coopie Pie". She then becomes excited when Coop inadvertently gives her a box of chocolates. Each time when Coop leaves and comes back via Kat's teleporter Phoebe either cries for him to come back or flirts with him.
After greeting him, Phoebe asks cutely to Coop if she and Millie could play what they're playing. She expresses pleasure when she has to go on Coop's team. When Dennis states the Coop picked the perfect spot for their flag, Phoebe sweetly adds "Of course it is. Coop picked it." When Dennis doesn't seem confident in Coop's mirror trap, Phoebe comforts and tells Coop not to worry and that it will be perfect.
Upon hearing from Millie that Coop is a "cat whisperer", Phoebe immediately goes over to Coop and seductively tries to get him to cheer up Honey Fluff. She seemed really proud when Coop's "powers" made Honey Fluff energetic, to the point where she told the whole street about it. When everyone describes their pet problems, Phoebe leans against Coop dramatically and tells him he's their only hope.
When Phoebe enters the school, she thanks Coop for wishing her good luck, not knowing he was talking to Millie. Soon after getting the audition, Phoebe grabs Coop's hand and states that she'll dedicate her song to him. She then snuggles and kisses him.
Shortly thereafter, she arrives at Coop's front yard and asks him lovingly if he's going to watch her performance. When Coop asks if she's nervous about the show, she states that with him as a lucky charm, nothing will go wrong. As she says this, she squeezes his cheek.
Late into the episode, she finally performs her tribute. It's intercut with Kat getting zapped violently, but it most likely went like this: His name is Coop and I love him. I sing this song for my Coop.
In the second opening, Phoebe blows a kiss in Coop's direction before smiling.
In the montage of Kat mind-controlling Coop, he makes him go to Phoebe's and have him get kissed by her. She, of course, takes it well, thinking it's legitimate.
In spite of being mad with him for wrecking the environment while battling Kat, she still greets him sweetly when the Greenie Girls arrive at his house.
Phoebe asks Coop if he could rub sunscreen on her back, and later asks if she could do the same to him. She later asks him to go swimming with her, even telling him he can use her snorkel.
When Phoebe arrives at Coop suffering heatstroke, she requests him to jump into her limo to go to her pool party. She later calls him over again while high diving.
Again, Phoebe calls Coop's name sweetly when she appears to him with her father.
After greeting Coop in her usual fashion, she then turns her attention to the scarf Fiona knitted for him. She doesn't like it and offers to style it for him. When told by her father to leave him alone, and that he "wears the wool of another woman", she screams in a jealous rage "WHO IS SHEEEEEEEE!?"
Simply put, Phoebe spends the majority of the episode being jealous of Coop and Fiona being together, doing everything she can to separate them. Aside from that, she does present to Coop bowling balls with their faces on them, as well as giving him SEVERAL gifts. In the end, Coop unintentionally saves Phoebe's life, which makes her gush heavily.
Phoebe ends up assuming that Coop called her his treasure.
Phoebe wants to join Coop in the family car so she can be closer to him and watch the film together.
Again, Phoebe is cheerleading for Coop during his soccer game. She even impersonates him with her foam head of Coop.
Throughout the short, Phoebe flirts with Coop and tries to get him to stay at her house. Firstly, she grabs a hold of his hands and states "It is nice of you to drop in." On the couch, she scoots closer to Coop. She then offers him a big tray of milk and cookies. When Kat sneaks some flowers into the milk glass, Phoebe assumes that Coop brought them to her and blushes deeply. She then attempts to kiss him several times, resulting in a wild goose chase around the house.