Update multiple subtitles photos in Mysql database - php

Question

I have a system that after uploading multiple photos it generates a subtitles field for each photo, I want to update the database of these subtitles. How to do this. My table in database - tb_fotos_portfolio table (id, portfolio_id, legenda, arquivo).
Obs .: It would be only the part of UPDATE the subtitles
<?php
$sql = "SELECT * FROM tb_fotos_portfolio WHERE id_portfolio = $id";
$query = $DB->Select($sql);
if (count($query) == 0) { ?>
<div class="box-body">
<h3 class="text-center text-danger" style="margin: 140px 0;">Imagem não enviada!</h3>
</div>
<?php } else { ?>
<div class="box-body no-padding">
<ul class="users-list clearfix">
<?php foreach($query as $item) { ?>
<li>
<a class="popup-link" href="../../../upload/portfolio/imagem/<?php echo $item['arquivo']; ?>">
<img src="../../../upload/portfolio/miniatura/<?php echo $item['arquivo']; ?>" alt="<?php echo $item['arquivo']; ?>"/>
<span class="users-list-name"><?php echo $item['arquivo']; ?></span>
</a>
<a class="btn btn-label btn-danger btn-xs" href="acoes.php?acao=deleteFotos&id=<?php echo $_GET['id'];?>&arquivo=<?php echo $item['arquivo'];?>"><i class="fal fa-trash-alt"></i>Excluir</a>
<span class="users-list-name"><?php echo $item['legenda']; ?></span>
<form id="" action="acoes.php?acao=legendas_fotos" method="post" enctype="multipart/form-data">
<input type="text" name="legenda[]" id="legenda" class="form-control" placeholder="Legenda" value="<?php echo $item['legenda']; ?>"/>
</li>
<?php } ?>
</ul><!-- /.users-list -->
</div>
<button type="submit" class="btn btn-success btn-label btn-sm"><i class="fa fa-check"></i> Atualizar Legendas</button>
</form>
acao.php
case 'legendas_fotos':
$legenda = $_POST['legenda'];
...
$sql = "UPDATE tb_fotos_portfolio SET legenda= $legenda ";
$vCampos = array('id'=>$id);
$DB->Execute($sql, $vCampos);
// Volta para o form
header("location:form.php?id=" . $id);
exit;
break