JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cloud.github.com/downloads/digitalBush/jquery.maskedinput/jquery.maskedinput-1.3.min.js"></script>
<select id="country" name="country">
    <option value='2'>Country (2 digit)</option>
    <option value='3'>Country (3 digit)</option>
</select>
<input id="phone" type="text"/>

JavaScript

jQuery(function($){
   $("#phone").mask("(99) 9999-9999");
    $("#country").change(function() {
        switch(this.value) {
            case "2":
                $("#phone").mask("(99) 9999-9999");
                break;
            case "3":
                $("#phone").mask("(999) 9999-9999");
                break;
        }
    });
});