Is communication between an engaged couple over the phone considered forbidden (haram) if it is within the bounds of decorum and religion, and not a daily occurrence, given that the fiancé is traveling and unable to return to complete the legitimate engagement until after three years?

The suitor is a stranger to the fiancée as long as the marriage contract has not been formalized. Therefore, it is not permissible to communicate through speech or messaging except out of necessity, and it should be limited to that necessity without excess. As for communication for reassurance or similar reasons without a valid need, it is a gateway to temptation and a means to corruption; for souls are weak, and Satan beautifies falsehood and gradually lures one towards what is forbidden.