On the install page, it says that Fortrabbit hosts a debian package for apt-get installation. http://debrepo.frbit.com/
Their version is Phalcon 1.2.3, so I emailed to ask if they were going to update it. They replied with:
Sorry, we do not use Debian PHP packages anymore ourselves (now custom build) so we've abandoned the repository. Thanks for getting in touch, though, i've updated the info on the site.
I just finished installing it on 6 servers :/ Now will have to uninstall and install manually! Doh!
So it'd be good if this page was edited otherwise users will be installing an old version that'll never update: http://phalcon.io/en/download