The calculated distance (air line) between Panghyŏn-dong and Ongjin is approximately 135 miles respectively 217 kilometers.
By car or train, the actual journey to Ongjin is certainly longer, as only the direct route (as the crow flies) between Panghyŏn-dong and Ongjin has been calculated here.
Air line (approximately)
217 kilometers
117 nautical miles