Fabio1 Thank you.
I would recommend re-creating the project so it's a new project type. The old one is not well supported by the new Visual Studio, and causes performance issues, especially in combination with TFS.
Go to File -> New -> Project, and look for
"PHP Project from Existing code", and recreate the project file in your existing project directory.
Please let me know if it helps, or if you'd need more help with it.