Angular phone number helper

controller.js

<input type="text" ng-model="user.phone" name="phone" ng-change="numberHelper()" ng-model-options="{allowInvalid:true}" ng-pattern="/^\+\d-\d{3}-\d{3}-\d{4}$/"/>

function numberHelper(){
    var phone = $scope.user.phone;
    var formattedPhone = phone;
    if(phone && !/^\+\d-\d{3}-\d{3}-\d{4}$/.test(phone)){
        phone = phone.replace(/[+-]/g, '');
        phone = '+' + phone.substr(0, 1)
                + (phone[1] ? '-' : '') + phone.substr(1, 3)
                + (phone[4] ? '-' : '') + phone.substr(4, 3)
                + (phone[7] ? '-' : '') + phone.substr(7, 4);
        formattedPhone = phone;
    }
    $scope.user.phone = formattedPhone;
}