How do you strip HTML from the node summary that appears on taxonomy node listing pages?
Within node--taxonomy.tpl.php, you could isolate the field data for your teaser or any field, depending on how you have that template set up, and apply the php strip_tags to that field data.

For example:

$teaser = render($content['body'][0]);
$textteaser = strip_tags($teaser);


This video is a great starting point for learning about the theming templates if that is new: Theming Fields and Nodes with Templates



One other idea is to isolate the div that wraps each teaser (if possible) and use jQuery to transform the content using the relevant CSS selector using .text() method.