<ion-view title="Login">
    <ion-content overflow-scroll="true" padding="true" class="has-header">
<?php include '../lib/init.php'; ?>
        <form class="list validate" ng-submit="submit()">
          <input type="hidden" name="action" value="login">
            <ion-list>
                <label class="item item-input">
                    <span class="input-label">Username</span>
                    <input type="text" ng-model="username" name="username" placeholder="">
                </label>
                <label class="item item-input">
                    <span class="input-label">Password</span>
                    <input type="password" ng-model="password" name="password" placeholder="">
                </label>
            </ion-list>
            <div class="spacer" style="height: 40px;"></div>
            <button type="submit" id="login-button4" class="button button-royal  button-block">Log in</button>
            <a ui-sref="register" id="login-button5" class="button button-royal  button-block button-clear">Dont have an account?</a>
            <a ui-sref="forgotPassword" id="login-button6" class="button button-royal  button-block button-clear">Forgot password?</a>
        </form>
    </ion-content>
</ion-view>

.controller('loginCtrl', function($scope, $state, $stateParams, $ionicPopup, $timeout) {

  //popup alert starts here
   $scope.showAlert = function(status,message) {
   var alertPopup = $ionicPopup.alert({
     title: status,
     template: message,
   });
 };
 //popup alert ends here


  $scope.submit = function() {
        if ($scope.username && $scope.password) {
          var url = 'my PHP file url';
          var username= $scope.username;
          var password= $scope.password;

          $scope.list = [];


          var dataString = 'username='+ username  + '&password=' + password;
          $scope.list.push(dataString);
          $scope.text = '';

          $http({
            type: "POST",
            url: url,
            data: dataString,
            success: function(data) {
            try
            {
              alert(data);
            }
            catch(e)
            {
              alert(data);
            }
            }
            });


        }
      };

})

.state('login', {
    url: '/login.php',
    templateUrl: 'templates/login.php',
    controller: 'loginCtrl'
  })

<form class="list validate" ng-submit="submit(username, password)">

$scope.submit = function(usr, pw) {
    if(!usr || !pw) return;

    //your stuff, not mine
    $scope.list = [];
    var dataString = 'username='+ usr + '&password=' + pw;
    $scope.text = '';

    var payload = {
        username: usr,
        password: pw
    };

    $http.post('path/to/php/file', payload).then(function(response) {
        //success
        alert(response.data);
    }).catch(function(response) {
        //an error occurred
        alert(response.data);
    });
}