input: from typing import List
  
  def concatenate_phrases(phrases: List[str]) -> str:
      """
      Take a list of phrases and concatenate them into a single string with commas and an "and" 
      before the last phrase.
      
      >>> concatenate_phrases(["apples", "bananas", "cherries"])
      "apples, bananas, and cherries"
      
      >>> concatenate_phrases(["one", "two"])
      "one and two"
      """
      if len(phrases) == 1:
          return phrases[0]
      return ', '.join(phrases[:-1]) + ' and ' + phrases[-1]
output:     if len(phrases) == 1:
          return phrases[0]
      return ', '.join(phrases[:-1]) + ' and ' + phrases[-1]