there are a few options:
quercus and ibm's ... ack - what was it called? they had a 'freeware' CMS that included their own implementation of PHP in Java.
I think there's another too, but there's quite a lot of oddities and assumptions that make PHP-based code not play well in the JVM.
ibm thingi was called "project zero"
btw i hear facebook is also looking to move to the jvm to ease some troubles with their hiphop approach
Don't think it solves this problem but Caucho Resin (Java EE server) should be able to run php as well.
I'm surprised there isn't something like JPHP yet to run PHP on the JVM.