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