3 phase transformer to output 2 wires
3 phase to single phase is not possible simply, you would need a lot of extra stuff, like phase shifters (load sensitive), or motor-generator (big'n'heavy), or rectifier-inverter (the preferred route these days).

If you want to stick to wiring, then there are two options.

You can use one of the output phases with respect to the star neutral. This will load only a single phase.

Or, you can use two phase outputs with respect to each other, without using the neutral line. This will get you sqrt(3) more voltage, but no more current. This will load two of the phases equally.