number.php

<?php
$number = '12345678';

function format($number, $len=3, $symbol='฿', $thousand=',', $right=true){
  $result = implode($thousand, array_reverse(array_map('strrev', str_split(strrev($number), $len))));
  return ($right)?$result.$symbol:$symbol.$result;
}

print format($number, '4');