import re

phone_book = '''
张三：138-1999-9101
李四：139-1998-5678
王五：138-1997-1234
'''

pattern = r'(\d{3})-(\d{4})-(\d{4})'

def mask_phone(match):
    return f'{match.group(1)}-****-{match.group(3)}'

masked = re.sub(pattern, mask_phone, phone_book)
print(masked)