As wrote luwes, you can add proxy_pass, and I deducted useful assets:

 location ~ \.php$ {
        proxy_pass $scheme://$host$uri/$args;
 }

1. Instead of using static link, you can write dynamically by variables $scheme, $host, $uri;
2. Following WordPress official Nginx Handbook and jamfire's example, variable $args should be preffered over $request_uri.