NSW Police Given New Powers to Download Phone Data During Roadside Stops and Arrests
(www.sydneycriminallawyers.com.au)
I have no clue what the law is in WA, let alone NSW. I only know the tech side. This software works by essentially taking a clone of the files on your phone and then brute-forcing it offline. If your phone is off, its contents are all encrypted and can't be accessed. At least today.
If you are the suspect of something big like murder etc, they'll keep your phone and probably will get into it eventually (like, years from now). And they'll persist that long. But, I doubt they'll commit those sorts of resources for a roadside stop.