[scotty]

You'd need to write a shim to the PHP API, like a REST or SOAP web service, or just a basic web page, then access that interface from your Zimlet via the Zimbra Proxy.

// call the web service to retrieve ABC
var service_url = 'http://....' + '?what=ABC';
var url = ZmZimletBase.PROXY + AjxStringUtil.urlComponentEncode(service_url);

AjxRpc.invoke(null, url, null, new AjxCallback(this, this._handler), true);

Your PHP would look like:

<?php
require 'API';

$what = $_REQUEST['what'];
if (valid_what($what)) {
  $resp = API_call($what);
  echo what_to_html($resp);
} else {
...
}