isPhoneNumber.py

def isPhoneNumber(text):
  if len(text) != 10:
    return False
  for i in range(0, 9):
    if not text[i].isdecimal():
      return False
    if text[0] == '0':
      return False
    return True

print('Is 8344777333 a phone number?')
print(isPhoneNumber('8344777333'))
print('Is 0123456789 a phone number?')
print(isPhoneNumber('0123456789'))