can anyone please tell me the between "have been" and "was"? Suppose my friends calls me and I reply the following. Are they interchangeable in the following context?
Note that I am not working at the moment of speaking. I have just finished it.
Past Simple was is used for something that finished in the past:
I worked there for five years - but I don't any more
Present perfect have been is used for something that started in the past, continued to the present and either is still happening, or has some lasting effect:
I have worked there for five years - and I still do.
In your sentence, if the speaker had literally just finished working when the phone rang, either would be acceptable.
If Paul is a colleague who wants the speaker to "quickly look something up" or whatever, they might use simple past to emphasize that they really have finished and doesn't want to start the computer, dig out files etc to help Paul.
If Paul is the speaker's boss, they might use present perfect to emphasize that they are hard-working and are (almost) still working.
You use "was" (past tense) for the events that occurred at a known time in the past and ended in the past.
Hey, Paul I was busy working in the morning.
You use "have been" (present perfect tense) for the events that occurred in an undefined time in the past and they or may not still last.
Hey, Paul I have been busy working all day.
The problem with your use of "have been" is the event is not continuing from the past so better usage would be simple past, "was". Both sentences refer to a task taking place only in the past. But then again, both refer to an event, not a thing, so technically should be past perfect.
