When we do the "Roman Number Problem" before, and this one after, it's like playing Elden Ring without mimic first, then play Elden Ring with mimic x).

Here the code :

import re
N = int(input())

for _ in range(N):
    current_number = input()
    
    pattern = r"^[789]{1}\d{9}$"
    
    yes_or_no = bool(re.match(pattern, current_number))
    
    if yes_or_no:
        print("YES")
    else:
        print("NO")

Without Regex:

for i in range(int(input())):
    inp= input()
    
    if len(inp) == 10 and (inp.startswith('7') or inp.startswith('8') or inp.startswith('9')) and inp.isnumeric():
        print("YES")
    else:
        print("NO")
				
				

Strange to see such a simple challenge following a few that are more complex. I'm used to challenges being increasingly more complex.

import re, sys

print('\n'.join(
  ['NO', 'YES']
  [re.match(r'^[789]\d{9}$', l) is not None]
  for l in sys.stdin.readlines()[1:])) 

n = int(input()) # Read number of test cases

for i in range(n):

ph_no = input()  # Read each mobile number

if len(ph_no) == 10 and ph_no[0] in ['7', '8', '9'] and ph_no.isdigit():
    print("YES")
else:
    print("NO")