Final Answer:
Phoebe promised to give Chandler her most prized possession, her "slinky."
Step-by-step explanation:
In a Season 5 episode titled "The One with All the Thanksgivings," Phoebe makes a deal with Chandler to quit smoking. As an incentive, she pledges to give him her most cherished possession, a slinky. Phoebe's quirky and unpredictable nature adds humor to the situation, and the slinky becomes a symbol of her commitment to supporting Chandler's efforts to quit smoking. This storyline showcases the unique dynamics of friendship among the characters on Friends. The promise of the slinky adds a comedic element to the serious issue of quitting smoking, highlighting Phoebe's eccentric personality and the camaraderie shared among the group.