The editor is set to accept the HTML code only and if you enter the PHP code, it will be commented out by the editor. If you want to get some custom output that you need to control using PHP, you can try adding a new attribute to accept a shortcode and then add the shortcode to the field when you insert the element to your page. This way you can control the output by that shortcode and use your custom PHP. I haven't tested this, but it should work fine.
Or you can use the dynamic field option as well.