To understand better php coding by debugging it is second to none to have code runner installed as extension in your own VS code editor.
In your editor from the extension sidebar when you type code runner, there will be some listing coming named with code runner. But you need to click on the one which has 6.9M+ downloads. 
After download is completed now you have the super power of debugging php in your integrated editor window.
To test your just written PHP code, you need to run code runner using your pre-defined keyboard shortcut.
Now this shortcut or key binding can be different from user to user. For myself I have created this as alt+v.
In order to create your own, you can do this by clicking Settings->Keyboard shortcuts and following screenshot
Finally, code debugging in action.
Just keep in mind that php needs to be added in your global environment system variable. Following is the screenshot:
Now you can enjoy debugging php code with super power. Happy Debugging!