I'm not at all familiar with that proxy service, but it may be relying on the host header value in order to route the connection to the Centos box. It's entirely possible the standard network libraries don't set this, whereas the mobile browser does. To test this assumption, try connecting to the IP address instead of the hostname using the browser.
I suggest you see if you can add a default proxy connection that doesn't rely on host headers (or anything similar).
Thanks,
Mike