PHP - Google Recaptcha

index.php

<?php

    if ( isset( $_POST['g-recaptcha-response'] ) ) {

        // ENVIA INFORMAÇÕES POR POST PARA TESTAR O CAPTCHA
        $result = file_get_contents( 'https://www.google.com/recaptcha/api/siteverify', false, stream_context_create( array(
            'http' => array(
                'header'  => "Content-type: application/x-www-form-urlencoded\r\n",
                'method'  => 'POST',
                'content' => http_build_query( array(
                    'response' => $_POST['g-recaptcha-response'],
                    'secret' => '6LfrOwcTAAAqwAAPLs7mGIKHlBw4qwfcKTJR9tVY_g-Dr'
                ) ),
            ),
        ) ) );

        $result = json_decode( preg_replace("/\n|\r| /", "", $result ) );

        if ( $result->success ) {
            // COLOQUE AQUI AS FUNÇÕES DO PHPMAILER
        }
    }

?>
<form method="post">
    <input type="text">
    <div class="g-recaptcha" data-sitekey="6LfrOwcTAqwgAAAAAGiqET2vLM2h84QdqwgC1w8hj0WyuB"></div>
    <script type="text/javascript"
            src="https://www.google.com/recaptcha/api.js?hl=pt-BR">
    </script>
    <button>enviar</button>
</form>