Thank you for the suggestion.
Sadly VSCode does not have API for different accessibility icons (I'll try to find their pending issue on github for reference).
As I know, php tools do not list private members outside its scope, but I'll double-check that. Also, protected members should not be listed. Although; since it is PHP, there are cases where even private/protected members can be used, so php tools might respect that.
Let me take a look at what can be done better; we should definitely add analysis for use of protected/private members outside the valid scope.