Phnom Penh eats early and on the street: noodle soup at dawn, a market lunch, and one proper Khmer dinner if you want to see what the cooking is capable of.
Psar Toul Tom Poung — the eating aisle
The Russian Market's food section, a row of stalls in the middle of the covered market doing noodle soup, rice plates and iced coffee for a couple of dollars. Go in the morning, while the market is still working rather than shopping.
Street 278 and the BKK1 lanes
The strip between Norodom and Sothearos holds most of the city's small independent restaurants and cafes, from Khmer kitchens to Japanese and Middle Eastern. Where you end up if you are staying in BKK1 and cannot face another riverfront menu.
Malis, Norodom Boulevard
The reference point for modern Khmer cooking, at No. 136 Norodom and open 6:30am to 10:30pm daily — which means a proper Khmer breakfast is on the table as well as dinner. Expensive by Phnom Penh standards and worth one meal.
Kuy teav, and eating before eight
Breakfast in Cambodia is kuy teav, a clear pork broth with rice noodles assembled to order at street stalls from about six in the morning. The stalls that do it well are a morning business, so it is the meal to plan a day around rather than eggs at the hotel.