iCloud backup

My wife got an iPhone 10 and went to verizon t o have them transfer the data from her old iPhone 6+. There were 2,000 photos on the iPhone 6+ but only 386 were copied to the new iPhone 10. iCloud backup only had 386 photos also. Verizon rep erased all data on the iPhone 6+ before verifying that all 2,000 photos were transferred to the new iPhone 10. Any idea how we get back the 1,614 lost photos? Apple rep. was no help at all...