How can I limit a string when parsing XML in PHP

I am writing a custom landing page in PHP parsing an XML product feed. The product descriptions are very long, as it goes into technical information and specifications, so need to be condensed to read the first 200 characters. hopefully with a read more link once 200 characters has been reached.

The code I have so far is:

<?php

$xml = simplexml_load_file('feed.xml');

foreach ($xml->item as $item) { ?>
<div class="row">
<div class="lhs">
    <h3><a href="<?php echo $item->link ?>"><?php echo $item->brand.' '.$item->title ?></a></h3>
    <p class="pri">&pound;<?php echo $item->price ?></p>
    <p><?php echo $item->description; ?></p>
    </div>
    <div class="rhs">
        <img src="<?php echo $item->image_link ?>" alt="<?php echo $item->title ?>" height="150" />
        </div>
        </div>  

<?php
}
?>

Please could anyone advise what else I need to add? I can follow basic patterns in PHP, I just need some guidance.

Many thanks in advance.