Make sure you have the correct compilation software
sudo yum install php-devel php-mysql gcc libtool pcre-devel
git clone --depth=1 git://github.com/phalcon/cphalcon.git
cd cphalcon/build
sudo ./install
echo "extension=phalcon.so" > /etc/php.d/20-phalcon.ini
echo Phalcon\Version::get();