Being 90 % a C# developer, I do love the way ReSharper analyzes my code in the background and immediately gives inline hints and warnings right in my code editor.
Today I came across a tool called "PHPStan" that seems to be a command line tool that analyzes PHP code for errors/issues/warning.
Suggestion
My suggestion is to include PHPStan (or other similar tools that might exist) into PHP Tools for Visual Studio and build a decent inline UI around it, just like ReSharper does for C# code.