I install it from packages.sury.org:
aptitude install php5.6-cli
aptitude install php5.6-fpm
aptitude install php5.6-mysql
aptitude install php5.6-curl
aptitude install php5.6-gd
aptitude install php5.6-imagick
aptitude install php5.6-intl
aptitude install php5.6-mbstring
aptitude install php5.6-xmlrpc
aptitude install php5.6-xsl
aptitude install php5.6-dev
aptitude install zip php5.6-zip
aptitude install php-pear
aptitude install php5.6-soap
pecl install timezonedb
aptitude install php5.6-mcrypt