`filter_input` validation

process-input.php

<?php

$recaptcha = filter_input(INPUT_POST, 'g-recaptcha-response', FILTER_CALLBACK, ['options' => validateReCaptcha('<your-secret-here>')]);
$phone = filter_input(INPUT_POST, 'phone', FILTER_CALLBACK, ['options' => validateTelephoneNumber()]);

validators.php

<?php

function validateReCaptcha($secret = '')
{
    return function ($field) use ($secret) {
        $recaptcha = new \ReCaptcha\ReCaptcha($secret);
        return $recaptcha->verify($field, $_SERVER['REMOTE_ADDR'])->isSuccess();
    };
}

function validateTelephoneNumber($strict = false, $strictRegex = '')
{
    return function ($string) use ($strict, $strictRegex) {
        $regex = $strictRegex ?: "/^(\d[\s-]?)?[\(\[\s-]{0,2}?\d{3}[\)\]\s-]{0,2}?\d{3}[\s-]?\d{4}$/i";
        if (!$strict) {
            return strlen(preg_replace("/[^0-9]/", "", $string)) >= 7;
        }
        return preg_match($regex, $string);
    };
}