What is the best way to go about passing a simple form from a .cfm page to .php
<form method="post" action="process.php">
<input type=text id="message" />
<input type="submit" />
</form>
That's the best way to do it, actually. As log as your process.php page is setup to accept FORM variables. That page can receive Form variables from any language/webserver.
I think you will want to use <input type="text" *name*="message" /> rather than id="message". Also, keep in mind that ColdFusion is not case-sensitive while PHP is -- although it should not be an issue in this case since CF will never see the form submit.
Kind of an older question, but thought I would point out that normally you would use an ajax call for this if you need to do something which isn't (easily) possible in ACF (adobe coldfusion). The advantage is that you can do all the frontend UI's in only one of the two languages.