Target URL parameter doesn't work

It is like any other URL parameter. It does work, but you need to use a valid structure for the query string.

If there’s already a parameter in a query string (including the one in the url when using default ugly permalinks) subsequent ones must be appended using an ampersand. The second parameter in your dummy url has a second question mark before the ampersand so the browser won’t be able to understand it.

Try it with this structure:

yoursite.com/?page_id=N&target=phone-numbers

I’ll probably add a note to the faq to document this next time I update the plugin.