Horrible Bosses

Nick Hendricks (Bateman) and Dale Arbus (Day) are friends who despise their bosses. Nick works at a financial firm for the sadistic David Harken (Spacey), who implies the possibility of a promotion for Nick for months, only to award it to himself. Dale is a dental assistant being sexually harassed by his boss, Dr. Julia Harris (Aniston); she threatens to tell his fiancee Stacy (Lindsay Sloane) that he had sex with her unless he actually has sex with her. Nick and Dale's accountant friend Kurt Buckman (Sudeikis) enjoys working for Jack Pellitt (Donald Sutherland) at a chemical company, but after Jack unexpectedly dies of a heart attack, the company is taken over by Jack's cocaine-addicted son Bobby (Farrell), whose apathy and incompetence threaten the future of the company.
At night, over drinks, Kurt jokingly suggests that their lives would be happier if their bosses were no longer around. Initially hesitant, they eventually agree to kill their employers. In search of a hitman, the trio meet Dean "Motherfuckah" Jones (Foxx), an ex-con who agrees to be their "murder consultant". Jones suggests that Dale, Kurt and Nick kill each other's bosses to hide their motive while making the deaths look like accidents.
The three reconnoiter Bobby's house, and Kurt steals Bobby's phone. They next go to Harken's house, where Kurt and Nick go inside while Dale waits in the car. Harken returns home and confronts Dale for littering, but then has an allergy attack from the peanut butter on the litter. Dale saves Harken by stabbing him with an EpiPen. Nick and Kurt think Dale is stabbing Harken to death and flee, with Kurt accidentally dropping Bobby's phone in Harken's bedroom. The next night, Kurt watches Julia's home, but she seduces and has sex with him. Nick and Dale reluctantly wait outside Bobby's and Harken's houses, respectively, to commit the murders, despite neither of them wanting to. Harken discovers Bobby's cellphone in his bedroom and uses it to find his address, suspecting his wife Rhonda (Julie Bowen) is having an affair. He drives over and kills Bobby, with Nick as a secret witness.
Nick flees at high speed, setting off a traffic camera. The trio meet to discuss their reservations about continuing with their plan. They are arrested by the police, who believe the camera footage makes them suspects in Bobby's murder. Lacking evidence, the police are forced to let the trio go free. The trio consult with Jones again, but learn that he never actually killed anyone, having been imprisoned for bootlegging the film Snow Falling on Cedars. Jones suggests that they get Harken to confess and secretly tape it. The three accidentally crash Harken's surprise birthday party, where Nick and Dale get Harken to confess to the murder before realizing that Kurt, who has the audio recorder, is elsewhere having sex with Rhonda. Harken threatens to kill all three for attempting to blackmail him. They flee by car, but Harken gives chase and repeatedly rams their vehicle. Believing they have committed a crime, the car's navigation-system operator remotely disables Kurt's car, allowing Harken to catch and hold them at gunpoint. Harken shoots himself in the leg as he boasts about his plan to frame them for murdering Bobby and attempting to kill him to get rid of the witness.
The police arrest Nick, Dale and Kurt, but the navigation-system operator, Gregory, reveals that it is his companies policy to record all conversations for quality assurance. Gregory plays the tape that has Harken confessing he murdered Pellitt. Harken is sentenced to 25 years to life in prison, while the friends get their charges waived. Nick is promoted to president of the company under a sadistic CEO, Kurt retains his job under a new boss, and Dale blackmails Julia into ending her harassment by convincing her to sexually harass a supposedly unconscious patient, while Jones secretly records the act.

Question: who steals Bobby's phone?
Answer: Kurt