The PHP extension has features, that restrict it from being installed as a web extension; therefore we're providing the "Web" version (as in the screenshot above).
The issue looks more like a bug on OpenVSX (https://github.com/eclipse/openvsx/issues) which provides the extension installer, and incorrectly(?) not giving the "Web" version to be installed.
May I ask you to fill in an issue there please, since we try to focus on Microsoft's marketplace at the moment?
thank you