</br> isn't a valid tag. There is no opening <br> tag for it, so with an XHTML doctype you would use a single sided tag which is <br/>. <B> doesn't exist in XHTML standards, but you can use <b>.
I won't follow links from work. If you mean that your string retrieved from storage should be broken into paragraphs on linefeeds, use this instead:
printf('<p class="paragraph">%s</p>', implode('</p><p>', explode("\n", trim($paragraph))));