If you have a scene created with Phoenix v.2 and you open it with version 3, it will keep all the old settings for you, some of which are not visible to newer versions and the result should be roughly the same.
If you try to replicate the same simulation setup with Phoenix v.3 and set all the parameters with the same values you would not obtain the same result. The new simulation will be different because Phoenix v.3 uses a new solver for liquids and fire/smoke.
