<?php
$in = 79817778833;
'/^(\d)(\d{3})(\d{3})(\d{2})(\d{2})$/',
'+\1(\2)\3-\4-\5',
(string)$in
);
echo($out);
PD9waHAKCiRpbiA9IDc5ODE3Nzc4ODMzOwokb3V0ID0gcHJlZ19yZXBsYWNlKAoJJy9eKFxkKShcZHszfSkoXGR7M30pKFxkezJ9KShcZHsyfSkkLycsCgknK1wxKFwyKVwzLVw0LVw1JywKCShzdHJpbmcpJGluCik7CgplY2hvKCRvdXQpOwo=