See the Phnom Penh City Bus Route Map:
Download the full size route map in English, or download the Khmer version: ផែនទីតម្រាយផ្លូវរត់រថយន្តក្រុងសាធារណៈរថយន្តក្រុងរាជធានីភ្នំពេញ.
The City Bus also has an app available that not only locates where you are, but also where the buses are and their movements.
Phnom Penh City Bus Android App
Phnom Penh City Bus Apple iStore
Don’t know how to ride the bus in Phnom Penh? Khmer lady Roth is your guide: