If somebody call me,after hey hello,what should I say , 1.what was the reason of your call? OR 2. What is the reason of your call?
As you want to ask the question during the call, which is happening in that current time, then you should use the present simple tense like this:
What is the reason for/of your call?
If it happened that you finished the call and met that person in a later time, then use the past simple tense as the call had been completed in some time in the past regardless of how much time had passed. It could be only a few minutes or seconds. As long as the event/action has finished, the past tense is used.
What was the reason for/of your call?
- Both of and for work, but "for" sounds better.
I think "reason for your call" sounds better than "reason of your call", but either verb tense works fine.
The act of placing the phone call was a single event which was completed in full, so from that point of view, the "call" is in the past, and you can ask, "what was the reason for your call?"
But you can also take the view that the "call" is a lasting activity that is going on throughout the conversation. If this is your interpretation, the "call" is in the present, and you can ask, "What is the reason for your call?"
So both "is" and "was" are equally correct. It just depends on your meaning for "call": making/placing the phone call? -- or conversing during the phone call?