The calculated distance (air line) between Ho Chi Minh City and Phnom Penh is approximately 127 miles respectively 204 kilometers.
By car or train, the actual journey to Phnom Penh is certainly longer, as only the direct route (as the crow flies) between Ho Chi Minh City and Phnom Penh has been calculated here.
Air line (approximately)
204 kilometers
110 nautical miles