This post is old. But just want to follow up that as of now (11-25-2008), Mor.ph is now offering PHP - currently in beta but worth a look...
I emailed Morph Exchange. They have plans to do PHP but they do not have a timeframe for it yet. For Java however, they it should be done within this year.
Perhaps there is a good reason for this. Soemthings are just hard/impossible to do in PHP.
Yahoo has publicly stated that they're going to be launching a service to compete with Google's App Engine using PHP as the programming language. No word was given on the timeframe.
Heroku is running on EC2. So put your PHP application on EC2.