MUTual EXclusion. Semaphore.

mutex.php

<?php declare(strict_types=1);

function phone_semaphore($phone, callable $callback)
{
    $sem = sem_get($phone, 1);

    if (sem_acquire($sem)) {
        $result = $callback();

        sem_release($sem);

        return $result;
    } else {
        throw new \Exception('Something went wrong..');
    }
}

$phone = 9999999999;

phone_semaphore($phone, function () {
    echo 'start'."\n";
    sleep(5);
    echo 'end'."\n";
});

nice man