<?php
$num = "011223333";
$res = preg_replace_callback(
'/(\d)\1*/', fn($match) => strlen($match[0]) . $match[0][0], $num
);
var_dump($res); //102243
<?php
$num = "011223333";
$res = preg_replace_callback(
'/(\d)\1*/', fn($match) => strlen($match[0]) . $match[0][0], $num
);
var_dump($res); //102243