Here are some strong contenders:
* "Phineas and Ferb Get Busted!" - This episode is known for Ferb's many lines, especially when he's trying to convince Phineas about the merits of a good old-fashioned adventure.
* "The Ballad of Badbeard" - Ferb's role as a pirate in this episode gives him more lines to deliver, and his dialogue is funny and memorable.
* "The Chronicles of Meap" - Ferb has more lines in this episode as he tries to help Meap find his home planet, including a memorable "Ferb, I'm gonna build a rocket."
* "Phineas and Ferb's Quantum Boogaloo" - While not necessarily more lines, Ferb's dialogue in this episode is highly memorable and significant to the plot.
Ultimately, the "most talkative" Ferb episode is subjective and open to interpretation. Regardless, these episodes are all good examples of Ferb's humor and character development.