apt-get install -y wget

# install PHP 5.6
echo "deb http://packages.dotdeb.org wheezy-php56 all" > /etc/apt/sources.list.d/dotdeb.org.list
echo "deb-src http://packages.dotdeb.org wheezy-php56 all" >> /etc/apt/sources.list.d/dotdeb.org.list
wget http://www.dotdeb.org/dotdeb.gpg -O - | apt-key add -

apt-get update

apt-get install php5

a2enmod php5

service apache2 restart

Links:
http://www.dotdeb.org/instructions/