Norman,
Most construction sites run on generator backup as it takes well over a year to get power connection from the local authority.
230V 3 phase is not the norm here, its 380V 3 phase and 230V single phase... Electrical sockets, lighting, drill machines available locally all work on 230V AC single phase, so i do doubt they will run the generator at a different voltage.
Just reconfirm in writing with the customer that he indeed needs 230V 3 phase, its not that uncommon here to find customers who dont know what they really need....