There is no national health insurance available in Cambodia, instead the best option is to take out a policy in your home country or with an international provider. Whilst general health care is reasonably inexpensive, standards are also very variable and services may be extremely limited in certain areas.
This increases the possibility of the necessity of medical evacuation to the nearest advanced providers of Bangkok and Singapore. However, this process of evacuation can be extremely expensive, and therefore it’s strongly recommended you ensure your policy includes medivac. Within this policy it should cover the eventuality of having to be airlifted in the case of serious illness or injury.