Joey: Know what was great? The way his smile was kinda crooked.
Phoebe: Yes! Like that man in the shoe!
Ross: What shoe?
Phoebe: From the nursery rhyme. There was a crooked man, who had a crooked smile, who lived in a shoe... for a while.
Phoebe is mixing two common nursery rhymes.
"There was a Crooked Man"
There was a crooked man and he walked a crooked mile,
He found a crooked sixpence upon a crooked stile.
He bought a crooked cat, which caught a crooked mouse.
And they all lived together in a little crooked house
"There was an Old Woman Who Lived in a Shoe"
There was an old woman who lived in a shoe.
She had so many children, she didn't know what to do.
She gave them some broth without any bread,
Then whipped them all soundly and put them to bed.