In Europe, the Model 3 has been delivered with the Gen2 Mobile Connector. Tesla is not selling plugs for the Gen2 Mobile Connector that support 3-phase as far as I know. People will have to see exactly what is supplied with the Model 3 cars in Australia, but I would not be surprised if the Mobile Connector is only supplied with a single phase plug adapter and no option is provided for Mobile 3-phase. The Tesla Wall Connector (or 3rd party equipment) is probably your only option for 3-phase.
The Model 3 will only take up to 16A three phase. I have not yet seen what charging limitation is imposed on SR+ in Europe. In North America it's 32A single phase instead of 48A single phase.
If the Gen1 Mobile connector was available to you and you got the Euro 3-phase adapter and an adapter to Australian 3-phase plug, you would get up to 16A 3-phase, which matches the capability of the car.