<?php if(!isset($opts['phplist_list_id'])) $opts['phplist_list_id'] = 1; ?>
<tr valign="top">
    <th scope="row">PHPList list ID</th>
    <td><input type="text" class="widefat" name="nsu_mailinglist[phplist_list_id]" value="<?php echo esc_attr($opts['phplist_list_id']); ?>" /></td>
</tr>