Hello.
This may not be the only method, but the way I know of aside from typing *.php would be to create a Working Set. You can select working set from the drop-down arrow at the right top of the open resource dialog.
When the Select Working Set window opens, you can click New and add working set by following the wizard. I used Resource as type (but I have Java specific Eclipse - you may see a PHP option in yours that would be better as I have a Java type in mine). Give this a name like "PHP Files" or "Web Files" and then you can select content and just ensure that you remove any unwanted extensions.
When you use open resources, as long as you have the working set selected any search you enter will only search the items in your working set thus excluding the PNG, SVN, etc. files.
Kevin
