HTML

phone number validation html

How about this? /(7|8|9)d{9}/

It starts by either looking for 7 or 8 or 9, and then followed by 9 digits.

html5 phone number validation with pattern and custom message

<input type="text" class="form-control" id="packet_name" name="packet_name" pattern="[^/:x22*?<>|]+" oninvalid="setCustomValidity('Invalid character in name:
  / : * ? < >.')" oninput="setCustomValidity('')" maxlength="100" required>