If jasmine provides wrong URL's for phantom you get no hint of whats going wrong.
In my case I had a setup where, for whatever reason, jasmine called the phantomrunner with wrong options where the host property contained the protocol twice, e.g. "host":"https://https://localhost:9000/"

In the jasmine.js setup function something like this would be helpful:

phantomjs.on('fail.load',function(url){
      grunt.log.writeln();
      grunt.warn('PhantomJS failed to request url ' + url , 90);
});