After years of running my own instance of WordPress, I finally configured my iPhone to upload images and whatnot. Turns out, I needed two things:

1. You have to know that the cell phone app wants the URL of the PHP xml RPC web address. It doesn’t assume anything when you enter in the address of your personal, self-hosted WordPress instance.
2. If you’re like me, you also probably need to up the limit on file uploads that is set by default in nginx.

server {
    listen 80;
    server_name blog.ignoranthack.me;
    location / {
            proxy_pass http://10.0.0.2:80;
            proxy_read_timeout 40;
            client_max_body_size 300m;
    }
}