I found this bundle of blooms on Kirirom Mountain, which is in the middle of Cambodia but above sea level where its cold. These misty mountains famous for Pinus Merkusii. An odd ecosystem, it supports bamboo and conifers. It has a cool Hawaiian climate. The flowers are one inch in diameter and have a gardenia scent. I guessed Michelia but it was too cold for that and besides it grows nowhere out of that cool mountain spot except maybe the Cardamoms. Since the rural poor sell all kinds of flower garlands, they would be ablle to grow this one if they can.i suspect it may only bloom together with the Pinus. Can it be Malus yunnanensis? Sorry I cant supply pix of cluster or leaf....
With that columnar syle possibly even a Synstylae (musk) rose, although the thickness of the filaments does not seem usual for a rose. Another possibility might be Pereskia, based on gross appearance of the flower only. In a tropical region there can be many thousands of native plant species still present (despite our efforts), add to that the possibility that the flowers shown are cultivated or naturalised...
Could it be Schima wallichii? I saw this in flower only last month in foothills of the Pang Sida National Park, Thailand, not far from the Cambodia border. The flowers were flatter than this, but that may just be due to the stage at which your Cambodian flowers were picked. The large stigma looks similar.