If you can't fix the PHP script, you can add a parameter to the URL, something like "&random=" || char(randominteger(1,9999999))
Assuming "random" isn't a parameter the PHP script knows about, PHP won't care, but the cache will see a different URL and you'll get fresh data.
You could use today(), if you wait more than a second, rather than random. Just something without spaces or special characters that changes.
Craige