Strip HTML tags and its contents

I'm using DOM to parse string. I need function that strips span tags and its contents. For example, if I have:

This is some text that contains photo.
<span class='title'> photobyile</span>

I would like function to return

This is some text that contains photo.

This is what I tried:

    $dom = new domDocument;
    $dom->loadHTML($string);
    $dom->preserveWhiteSpace = false;
    $spans = $dom->getElementsByTagName('span');

    foreach($spans as $span)
    {
        $naslov = $span->nodeValue; 
        echo $naslov;

        $string = preg_replace("/$naslov/", " ", $string);
    }

I'm aware that $span->nodeValue returns value of span tag and not whole tag, but I don't know how to get whole tag, together with class name.

Thanks, Ile