<div class="row contact">
<div class="col-lg-6 col-sm-6 ">

<form id="form" method="post" action="mail/phpmailer.php">
        <input type="text" class="form-control" placeholder="Nome completo:" name="nome">
        <input type="text" class="form-control" placeholder="E-mail:" name="email">
        <input type="text" class="form-control" placeholder="Número para contato:" name="num">
        <textarea rows="6" class="form-control" placeholder="Digite sua mensagem" name="msg"></textarea>
        <input type="button" class="btn btn-success" name="enviar" value="Enviar">
</form>
</div>
</div>

<?php
require 'phpmailer/PHPMailerAutoload.php';

$mail = new PHPMailer();
$mail->setLanguage('pt');

$from = '-@-.com.br';
$fromName = '-';

$host ='smtp.umbler.com';
$username ='-@-.com.br';
$password ='-';
$port =587;
$secure =false;

$mail->isSMTP();
$mail->Host = $host;
$mail->SMTPAuth = true;
$mail->Username = $username;
$mail->Password = $password;
$mail->Port = $port;
$mail->SMTPSecure = $secure;

$mail->From = $from;
$mail->FromName = $fromName;
$mail->addReplyTo($from, $fromName);

$mail->addAddress('-@-.com', '-');

$mail->isHTML(true);
$mail->CharSet = 'utf-8';
$mail->WordWrap = 70;

$mail->Subject = 'Contato ';
$mail->Body    = 'Nome: ' .$_POST['nome'] . 'Email: ' . $_POST['email'] . 'Numero: ' . $_POST['num'];
$mail->AltBody    = $_POST['msg'];

$send = $mail->Send();

if($send)
    echo 'E-mail enviado com sucesso!';
else
    echo 'Erro : '.$mail->ErrorInfo;
?>

if($send){
  echo 'E-mail enviado com sucesso!';
  echo '<meta http-equiv="refresh" content="3;URL="paginadoformulario.HTML">';
}
else{
    echo 'Erro : '.$mail->ErrorInfo;
}

<form id="form-ajax" method="POST" action="sua pagina aqui">

if($send){
    echo 'E-mail enviado com sucesso!';
    sleep(1);
    echo '<script>window.history.go(-1)</script>';
} else {
    echo 'Erro : '.$mail->ErrorInfo;
}