Rob Donnen appeared in "The One After The Superbowl, Part 1". He schedules performers for the children's libraries around the city and asks Phoebe to perform for them. The two of them have an attraction to each other and Phoebe's nerves about playing in front of people who actually listen disappear after Rob first kisses her.
Not knowing the subject matter of Phoebe's songs, Rob (along with the children's parents) is shocked when she sings songs about dying and sex to the kids. Rob suggests that shes play more songs about barnyard animals, which Phoebe says she can do. She ends up singing a song about slaughtering of farm animals for food and is subsequently fired because of it.
Rob's relationship with Phoebe more or less ends at that point.