Pretty often, people mistype the phone number: forget one figure, or type more than enough by duplicating a figure, especially with repeating figures. To decrease such cases, would be great to implement the indicator that informs the user that the currently entered phone number is valid - some check mark or color highlight. From the code side, we can easily check if the number of figures is enough to be the full number, or less, or more, right? So, let's just indicate this!