input: Write a function to phrase each word in a sentence with the same first letter.
  assert phrase_words('Hello World Goodbye Mars') == ['HHello', 'WWorld', 'GGoodbye', 'MMars']
  assert phrase_words('Happy Birthday To You') == ['HHappy', 'BBirthday', 'TTo', 'YYou']
  assert phrase_words('Python Programming Is Fun') == ['PPython', 'PProgramming', 'IIs', 'FFun']
output: def phrase_words(sentence):
      return [word[0] + word for word in sentence.split()]