Use o seguinte conjunto de comandos para adicionar PPA para PHP 7 em seu sistema Ubuntu e instalá-lo.

$ sudo apt-get install python-software-properties
$ sudo add-apt-repository ppa:ondrej/php-7.0
$ sudo apt-get update
$ sudo apt-get install -y php7.0

Módulos disponiveis:
$ sudo apt-cache search php7-* 


php7.0-common - Common files for packages built from the PHP source
libapache2-mod-php7.0 - server-side, HTML-embedded scripting language (Apache2)
php7.0-cgi - server-side, HTML-embedded scripting language (CGI binary)
php7.0-cli - command-line interpreter for the PHP scripting language
php7.0-phpdbg - server-side, HTML-embedded scripting language (PHPDBG binary)
php7.0-fpm - server-side, HTML-embedded scripting language (FPM-CGI binary)
libphp7.0-embed - HTML-embedded scripting language (Embedded SAPI library)
php7.0-dev - Files for PHP7.0 module development
php7.0-dbg - Debug symbols for PHP7.0
php7.0-curl - CURL module for PHP
php7.0-gd - GD module for PHP
php7.0-imap - IMAP module for PHP
php7.0-intl - Internationalisation module for PHP
php7.0-ldap - LDAP module for PHP
php7.0-pgsql - PostgreSQL module for PHP
php7.0-pspell - pspell module for PHP
php7.0-recode - recode module for PHP
php7.0-snmp - SNMP module for PHP
php7.0-tidy - tidy module for PHP
php7.0-json - JSON module for PHP
php-all-dev - package depending on all supported PHP development packages
php7.0-sybase - Sybase module for PHP
php7.0-modules-source - PHP 7.0 modules source package
php7.0-sqlite3 - SQLite3 module for PHP
php7.0-mysql - MySQL module for PHP
php7.0-opcache - Zend OpCache module for PHP