Is it possible to define the main difference between ”out” and ”off” as particles when they are part of a phrasal verb? I have read the definitions given in the Collins dictionary. And they are many and varied. Is it possible to explain why for example ”out” and not ”off” is used in this or that phrasal verb? For example, to blow off and not blow out? Is it possible to define the etymology of phrasal verbs?
As a native BrE speaker, I regularly encounter variants of the form verb + particle. If you watched TV cooking programmes in the 1990s you would have heard frequent reference to things beings "cooked off" or "fried off". In my own kitchen I only cook and fry, never fry off. I asked a friend who is a chef why the 'off' was there: his reply was that that is how chefs speak to each other. Some people who are not chefs have a "fry up". Some people cook up a stew or boil down a sauce. Other times dishes are cooked down, or boiled up, or dried out or baked in.
It might be possible for some linguist to write rules that describe the process of adding particles to verbs in these contexts, but even if that were done those rules would be descriptive rather than prescriptive.
So, in my opinion it is not possible to define the difference between such particles other than purely descriptively, if then. You just have to know.