Can Nginx take the port for proxy_pass from the request?

Question

Nginx

Nginx works like a normal proxy. Receives requests of the following form:
GET http://example.org/page.html
/etc/nginx/conf.d/proxy.conf:

server {
        listen 3128;
        resolver 8.8.8.8;
        server_name _;
        location / {
                proxy_pass $scheme://$host$uri;
        }
}

The problem is that the request may contain a non-standard port (for example, GET example.org :81 /page.html), and Nginx will still send it to port 80.
If you write "proxy_pass $request;", then Nginx will respond to any requests ( with or without a port) starts swearing in the logs:

invalid URL prefix in "GET http://example.org/page.html HTTP/1.1"

Is it possible to teach Nginx to connect to the port specified in the request?