The One Where Monica Gets a Roommate - S1-E1
Audio problem: When Phoebe says "I just don't want her to go through what I went through with Carl" the camera cuts to Chandler's reaction. When you look at the bottom Phoebe's mouth is moving even though she's not speaking. (00:01:39)
The One Where Monica Gets a Roommate - S1-E1
Audio problem: The camera cuts briefly to Chandler as the friends are discussing Monica's love life. During this very brief time, you can see Phoebe's mouth moving but there is no audio of her voice, and Monica's voice is heard talking in the background instead. (00:01:10)
Answer: The statements that she's contradicting (that it is common, it happens to every guy, and it's not a big deal), are the things that a woman commonly says to a man who is suffering from erectile difficulty, typically to assuage his bruised ego. However, most men do not believe that these statements are true, as evidenced by Chandler's outburst. He's so caught up in the proof that women are lying about it that he gives himself away.
Rooster of Doom