[j0hnik]

<style>
	.phone_number_xxxx{
		padding-right:10px;
	}
</style>
	<span class="phone_number">+74951182647<span class="phone_number_active">Показать</span></span><br>
	<span class="phone_number">+74951182647<span class="phone_number_active">Показать</span></span>
	<script>
		[].forEach.call(document.querySelectorAll('.phone_number'),function(el){
			var hide = /(\d{4})[А-Я\s]/.exec(el.textContent)[1];
			el.innerHTML = el.innerHTML.replace(hide, '');
			var btn = el.querySelector('.phone_number_active');
			btn.insertAdjacentHTML('beforebegin', '<span class="phone_number_xxxx">xxxx</span>');
			var xxx = el.querySelector('.phone_number_xxxx');
			btn.onclick = function(){
				xxx.textContent = xxx.textContent.replace(/xxxx/, hide);
			};
		});
</script>