Visual Studio 2017 or higher

Go to Visual Studio's Extension Manager in Tools | Extensions and Updates (Visual Studio 2017) or Extensions | Manage Extensions (Visual Studio 2019 or newer).

Uninstall from VS

Any new installation, update or removal requires restarting Visual Studio. The user is notified about that, and it is recommended to perform installations or updates while all Visual Studio instances are closed.

Visual Studio 2010 - 2015

PHP Tools for Visual Studio is installed through the Windows Installer. Use Programs and Features in Windows Control Panel for repair, change or uninstall.

Uninstall from Control Panel

Note: The extension is listed in Visual Studio in Tools | Extension Manager without the option to uninstall.