The calculated distance (air line) between Kampong Thom and Phnom Penh is approximately 79 miles respectively 128 kilometers.
By car or train, the actual journey to Phnom Penh is certainly longer, as only the direct route (as the crow flies) between Kampong Thom and Phnom Penh has been calculated here.
Air line (approximately)
128 kilometers
69 nautical miles