Phone reception on the highway is not great and I can't see it being much better out to sea. My guess is it Would be okay to Cape Conran then patchy until off Mallacoota, then not much again until within range of Eden. Your best best would be a phone call to Coastal Patrol Eden.
Sailing AUS Coast and expect mobil phone reception, Do NOT expect that. You might get patches here and there but don't relay on it. Even external aerial is slim improvement . Active electronic mob. phone extender is not available here. Than the only option is satellite phone and log in with Coast Guard.
Off Jervis Bay 3g range is about 10nm. My yacht has a masthead phone aerial which the previous owner reckons they had continuous contact all the way to Tasmania. Plug does not suit my phone so I don't know if it still would.