JSFiddle - React, Tailwind, and code Playground

HTML

<a href="" class="phone">+7 (000) 000-00-00</a>

CSS

a{
  color:#000;
  text-decoration:none;
}

JavaScript

$(document).ready(function() {
  var str = $('.phone').text().slice(-9);
  $('.phone').html('+7 (000) <b>'+str+'</b>');
});