Final answer:
In 'The Office' S5E10, Phyllis gains control over the Party Planning Committee because she learns of Angela's affair with Dwight and uses the information to take charge of organizing the Moroccan Christmas party, leaving Angela without a say.
Step-by-step explanation:
In the episode 'Moroccan Christmas' from season 5 of the television show The Office, Phyllis takes charge of the Party Planning Committee because she had previously gained leverage over Angela. Phyllis discovered a secret about Angela's affair with Dwight, which she uses to take control of the office party planning duties. As a result, despite Angela's traditional role in the committee, she doesn't have a say in the decisions regarding the Moroccan Christmas party.