Phalcon 2.0 compiles with all debug symbols enabled by default which creates a big .so, if you want a smaller .so, from a clean clone of Phalcon, you can compile it this way:
cd cphalcon/ext
git checkout 2.0.0
export CFLAGS="-O2 -flto -fvisibility=hidden"
phpize
./configure --enable-phalcon
make
sudo make install