When I click on any file eg php file it open by default in gedit I want that it will open by default in quanta plus
Right click on the file -> select 'Properties' -> go to the 'Open With' tab -> select the text editor of your choice from the list.
I believe that will make the text editor you choose the default for that particular file type. You'll have to repeat those steps for every file type though (e.g. plain text file, .log, .txt, etc.)
Just saw, but this question was already answered in a general form here: How do I change the default text editor?