If you want just the text as output, use strip_tags($content).
You might find that line breaks are missing, causing the text to look confusing.
If you're lucky your can use ln2br($content).
If there were no line breaks in the html, you will have to make a function to use before strip_tags and ln2br, that searches for the end tags of elements such as </h1> to </h6>, </p>, </li>, </ul> etc...
Just use str_replace or something to replace those tags with the same tag + "\n", like this:
$content = str_replace("</p>", "</p>\n", $content);
$content = strip_tags($content);
$content = ln2br($content);
If you display the text in a textarea, you can omit ln2br.