Open preferences window and go to PHP -> Code Style -> Formatter and there you click on “Edit…” of the current selected profile:
Now go to the tab called “Line Wrapping” and there set the field “Maximum line width” to your wished line width:
After click on the tab called “Comments” and there set the field “Maximum line width for comments” also to 120:
Click Ok and then Apply. Now we have to make the line visible to the correct width to do that make sure you have opened your preferences still and then General -> Editors -> Text Editors there you have field “Print margin column” change this to your new value:
Now click on Ok and then you are done.