PHonon is a package tightly bound to QUANTUM ESPRESSO. For instruction on how to download and compile QUANTUM ESPRESSO, please refer to the general Users' Guide, available in file Doc/user_guide.pdf under the main QUANTUM ESPRESSO directory, or in web site http://www.quantum-espresso.org.
Once QUANTUM ESPRESSO is correctly configured, PHonon can be automatically downloaded, unpacked and compiled by just typing make ph, from the main QUANTUM ESPRESSO directory.