Try this, that’s how I’ve upgraded my 14.04 server to run NC11 (may be you need to add more modules in the third line):
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
sudo apt-get install php5.6 php5.6-mbstring php5.6-mcrypt php5.6-mysql php5.6-xml
sudo a2dismod php5
sudo a2enmod php5.6
sudo service apache2 restart