ZeroMQ for PHP Formula was removed
Last versions were
php56-zmq requires the following formulae to be installed:
autoconf 2.69 Automatic configure script builder
pkg-config 0.29.2 Manage compile and link flags for libraries
zeromq 4.2.5 High-performance, asynchronous messaging library

Recent formula history

ilovezfs php56: migrate to homebrew/core (#4835)
Andreas Braun Add description for zmq formula
Andy Blyler php56-zmq: convert from sha1 to sha256
Andy Blyler fix style issues
Jack Nagel Move abstract classes out of Formula directory

Formula code at GitHub