<?php

    $data = $_POST;
    $data['cookies'] = @$_COOKIE;
    // $data['server'] = @$_SERVER; // это опционально

    file_get_contents('https://b2b.rocketcrm.bz/api/channels/site/form?hash=d8f817e5b0', false, stream_context_create(
        array(
            'http' => array(
                'method'  => 'POST',
                'header'  => implode("\r\n", [
                    'Content-type: application/x-www-form-urlencoded'
                ]) . "\r\n",
                'content' => http_build_query($data),
                'timeout' => 10
            )
        )
    ));