Lost all contacts after updating company email

A friend of mine uses a company provided phone with a company provided email. He recently switched to a new phone and we managed to get all of his contacts updated through iCloud, but they just vanished except for a few he recently added. With the company email the password must be changed every 3 months, so he has changed his password recently.

Could that be the cause of the missing contacts? If so, how do I help him update that? Could I possibly prevent it from happening again? If not, what else could be the cause?