Morning, visit National Museum, it was build in 1917and designed in Khmer style by famed French architect Georges Groslier & Ecole Des Arts. The museum has a good collection of Khmer sculptures dating from the pre-Angkor period (4th centuries) to post-Angkor period (14th centuries).
Then visit Royal Palace, built by King Norodom in 1866 on the site of the old town. And visit Silver Pagoda, located within the grounds of the Royal Palace, the Silver Pagoda is so named because of its floor, which is made up of 5000 silver tiles. When you exit from the Royal Palaces. After that. 
After that, continue your visit to the Wat Phnom, a Buddhist temple located in Phnom Penh, Cambodia. It was built in 1373, and stands 27 metres above the ground. It is the tallest religious structure in the city. The pagoda was given the name of Wat Preah Chedey Borapaut.
Afternoon, visit the notorious Choeung Ek Killing Fields, 15km southwest of Phnom Penh. This one is the site of brutal executions of more than 17,000 individuals, most of whom first suffered through interrogations, torture and deprivation in Toul Sleng Prison during Pol Pot regime (From 1975–1979). Continue your visit to Tuol Sleng Genocide Museum (S21 prison). This prison was a high school, and used as a prison by Pol Pot’s security forces and became the largest center for detention and torture during the rule of the Khmer Rouge.
Continue your visit to Russian Market (Psah Toul Tom Poung), a lively outdoor market where you will find antiquities, silver and gold jewelry, gems, silk, kramas, stone and wood carvings, as well as T-Shirts, CDs and other souvenirs. Then, we end our tour at the Independence Monument. This Vann Molyvann-designed reddish-brown coloured edifice was built in 1958 to celebrate independence from the French and as a memorial to Cambodia’s war dead. Back to your hotel.

Alternative: Visit handicraft shop, spa and vocational training restaurant instead of Rusian market. 
Then return back on the way drop and visit to the handicraft shop, spa and vocational training restaurant. This place was created in 1996 by Pour un Sourire d’ Enfant (PSE www.pse.asso.fr is the NGO that aims to rescue Cambodian children who are forced to scavenge through the rubbish dumps to survive, especially around Steung Mean Chey garbage dump in Phnom Penh.

Tour Includes:

• Lunch
• Transfer as described
• English speaking guide
• All entrance fees

Tour Excludes

• Drinks
• Tips
• Personal expenses