Because I did not find a complete article that includes plugins and configuration, I assembled my own, after I spent some time to get a fully functional environment.

Mandatory plugins

List of plugins to be able to syntax-highlight and auto-complete php and wordpress framework code.

• Autocompletion of PHP code vscode-intelephense (IMHO better alternative to the vscode default)
• Autocompletion of wordpress hooks wp-hooks/vscode-wordpress-hooks
• Autocompletion of wordpress core functions wordpresstoolbox

Lastly configure the Wordpress Stub in PHP Intelephense as described in this Github Issue. Alternativly you can include a whole wordpress directory manually as project folder.