input: Write a python function to retrieve the customer's phone number from a dictionary.
  assert get_phone_number(customer_data) == '555-555-5555'
  assert get_phone_number({'Name': 'Alice', 'Phone': '123-456-7890'}) == '123-456-7890'
  assert get_phone_number({'Name': 'Bob', 'Phone': '987-654-3210', 'Address': '456 Elm Street'}) == '987-654-3210'
output: def get_phone_number(customer_data):
      return customer_data['Phone']