very basic phone number format for display

phone-format-basic.php

<?php
/**
 *   Phone Number Format
 *   - used to display phone numbers from a WooCommerce database
 *   - assumes local US numbers
 *   - very basic: removes non-digit characters, +1, adds dashes
 *   - props for base function to https://arjunphp.com/format-phone-number-using-php/
 *   - props for "+1" to https://simplysmartmedia.com/2013/11/php-phone-number-formatting-function/
 */
private static function phone_number_format ( $number ) {
   // allow only digits, remove all other characters
   $number = preg_replace("/[^\d]/","",$number);

   // remove "1" if it's the first character
   $number = preg_replace("/^1/", "", $number);

   // check number length; add dashes iff it has 10 digits
   $length = strlen($number);
   if ( $length == 10 ) {
      $number = preg_replace("/^1?(\d{3})(\d{3})(\d{4})$/", "$1-$2-$3", $number);
   }
   return $number;
}
?>