$ sudo add-apt-repository ppa:ondrej/php
$ sudo apt-get update
$ sudo apt-get upgrade php

$ php -v
Cannot load Xdebug - it was already loaded
PHP 7.1.8-2+ubuntu16.04.1+deb.sury.org+4 (cli) (built: Aug  4 2017 13:04:12) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies
    with Zend OPcache v7.1.8-2+ubuntu16.04.1+deb.sury.org+4, Copyright (c) 1999-2017, by Zend Technologies
    with Xdebug v2.5.5, Copyright (c) 2002-2017, by Derick Rethans