<?php
while ($user = $stmt->fetch( PDO::FETCH_ASSOC ))
echo '
<div class="stroka_klient">
<div class="id_klient">'.$user['K_id'].'</div>
<div class="name_klient">'.$user['K_name'].'</div>
<div class="telephone_klient">'.$user['K_phone'].'</div>
<div class="email_klient">'.$user['K_mail'].'</div>
</div>';
?>