I'm trying to build phalcon-2 on centos 6.9. php is 5.3.3, gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18)
yum install -y httpd php php-mysql php-devel git gcc libtool pcre-devel
unzip
wget https://github.com/phalcon/cphalcon/archive/phalcon-v2.0.13.zip
unzip phalcon-v2.0.13.zip
cd cphalcon-phalcon-v2.0.13/build
./install
I installed php 5.3.33 from sources and it worked.