The streets in Phnom Penh are non-sequentially numbered and my attempts to find out why have come up empty. They do seem to follow a certain logic – at least in the eastern half of the city the streets are numbered lower to the north, running south at intervals of approximately 4+ per block. West to east is a little less clear. Main roads are typically referred to by name, not number (Sihanouk, Monivong, Mao Tse Toung) . A Phnom Penh Post article explains in more detail.
Previously Google removed street numbers from their maps of Phnom Penh in favor of the Khmer road names, which colloquially are rarely used: directions are given by landmark and through conversation or turn by turn, not by intersection (Wat Lam Ka… Psar Toul Tom Pong… Riverside…)
The house numbers however, probably due to the elimination and then re-instatement of private ownership? … are another story, seemingly arbitrary and designed to confuse rather than direct. Coupled with a lack of street signs, finding an office or flat for the first time can become an unintentional and time consuming adventure… Most corners are not signed, leaving you to turn down a street to figure out which street you are on…
Often 3G phone maps don’t update quite fast enough to pinpoint your location. You end up doing laps around the block to find a specific house number or to locate the right ‘blue gate’ of your friend’s house. I drove down a street near my house to check out the variety of house signs and whether the street was signed with its number (it wasn’t). This made me realize that I navigate here by memory and have largely given up on using the street or house numbers to get around.