I had a hell of a time trying to figure out how to call phpBay from a theme file rather than by using the shortcode. After sending a quick email over to the developer, he eventually gave me this code which works like a charm:
<!– start of ebay–>
<!–?php $text='[phpbay]"", "", "", ""[/phpbay]'; echo phpBayPro($text) . ""; ?–>
<!– end of ebay –>
I hope this helps anyone else who is trying to figure this out.