<?php echo (strlen($description) > 300 ? utf8_substr(strip_tags(html_entity_decode($description, ENT_QUOTES, 'UTF-8')), 0, 100) . '..' : $description); ?>

$arr = preg_split('/(</p>|<br>)K/', $str);

$str = implode('', array_slice($arr, 0, нужное кол-во));