Hi Roland,
Can you watch the network tab and see if the request is going through the proxy or not? Also, try to proxy a non-secure resource just to see if the proxy works without passing credentials. I do not have the PHP proxy active, but I can get it to work with the DotNet proxy and a secure Feature Layer as well as a non-secured basemap request with the urlUtils.addProxyRule:
require([
"esri/Map",
"esri/config",
"esri/request",
"esri/core/urlUtils",
"esri/layers/FeatureLayer",
"esri/core/Accessor",
"dojo/domReady!"
], function (Map, esriConfig, request, urlUtils, FeatureLayer){
urlUtils.addProxyRule({
urlPrefix : "sampleserver6.arcgisonline.com",
proxyUrl : "/proxy/proxy.ashx"
});
-Noah