In AngularJS, why isn't my post data being used by my php?

Question

I sending some form data using:

.controller('signupController',function($scope,$http){

$scope.submitSignup = function(){
    var firstLast = $scope.firstLast;
    var email = $scope.email;
    var phone = $scope.phone;
    var zip = $scope.zip;
    var signup = $scope.signup;

    $http({
        method: 'POST',
        url: '../process.php',
        headers: {
            'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'
        },
        data: {
            firstLast:firstLast, 
            email:email, 
            phone:phone, 
            zip:zip
        }
    })
    .then(function(res){
        console.log(res);
    });
}

})

If I return my query I get:

data: "INSERT INTO signups (signup_name,email,phone,zip) VALUES ('','','','')"

As you can see my values are empty. However, if I return a $_POST values I get that it's null and I can get a message that my values are undefined if I turn on php errors.

I've set the header content-type and they usually avoids this issue.