Sorry for the late reply.
I tried the last link you provided and get this error when trying to install:
Activating extension 'DEVSENSE.phptools-vscode' failed:
Creating workers from remote extensions is currently not supported..
Tested code-server version:
Just tried to install it using the command-line, and that seems to have worked.
code-server --install-extension ./phptools-vscode-web-1.7.8717.vsix