input: Write a function to extract phone numbers from a given list that start with '08'. The function should return a new list containing only these phone numbers. If the input list is empty, the function should return an empty list.
  assert extract_phone_numbers(['0834567', '0945678', '07123456', '08901234', '07890123'])==['0834567', '08901234']
  assert extract_phone_numbers(['08123', '08456', '08789'])==['08123', '08456', '08789']
  assert extract_phone_numbers(['09123', '07456', '06789'])==[]
  assert extract_phone_numbers([])==[]
output: def extract_phone_numbers(phone_list):
      return [num for num in phone_list if num.startswith('08')]