I think you need to skip -X
:
screen -d -m 'php process.php param1 param2'
It's also useful to give the session a name, especially if you're starting several:
screen -d -m -S mysession 'php process.php param1 param2'
-X
is for sending commands to screen
itself.
See also: this QA here on SO
Additional explanation
The started screen
session will only exist as long as your command is running. When php process.php ...
exits, screen
will also exit.