- preg_match: documentation ( source)
- strip_tags: documentation ( source)
<?php
$html = '<font face="Arial, Helvetica, sans-serif" color="#000099"><strong><font
color="#660000">Account Number</font></strong><font color="#660000">: 033<br>
<strong>Account Name</strong>: More text here<br>';
echo preg_match('~Account Number:\s*\K\d+~', strip_tags($html), $match) ? $match[0] : 'No Account Number Found';