I remember that episode. It has nothing to do with the words itself, they're mimicking the way Chandler talks and laughing at his unique intonation. Chandler tends to draw out and emphasize certain words, and his pitch even goes high sometimes. For example, if you go back and listen to that scene again, for the phrase "could that report be any later?" he really emphasizes and draws out the word "be" and his pitch is higher too. And when he's trying to say "that is so not true," he can't help but emphasize the word "so" and he gives up saying it altogether because he's just proving their point.

Chandler is being made fun of at his work by his employees. His employees are making fun of him because he is their boss. They are making fun of him by impersonating him (this is what Phoebe means by "they do you". "do" in this case means "impersonate" or "mimic" or "pretend to be"). When Ross says "the hills are alive with the sound of music", he is saying it in a voice that sounds like Chandler's voice, in order to poke fun at how Chandler talks. The same thing happens with "my scone". It's been a long time since I've seen this episode so I could be slightly off on some things.I hope this makes sense though. Feel free to message me if I didn't explain something well!