If an owner wants to make changes to a utility (as opposed to repair a broken utility) service that only benefits him I’d say he has to pay the full amount.
Must admit I don’t know what a phone control box is as I’ve no idea where mine is and I don’t really care.
As it’s a 2 lot Strata assuming the entitlement is 50-50 unless your neighbor agrees to pay for the change in full you can deny his request.