Reply To: Specific format

I developed a pattern

$out .= '<label>' . __('Phone Number (format (506) 555-5555)' , 'connections_form' ) . '</label> <input type="tel" pattern="[\(]\d{3}[\)]\d{3}[\-]\d{4}" name="phone[::FIELD::][number]" value="" style="width: 30%"/>' . "\n";

But I still can add any type of number for the phone number. Where else do I need to edit Connections Form so I can force people to use that specific format?