How to trace virtual phone number?

If you have suffered some sort of harm from the calls (e.g. death threats or harassment), it is in theory possible to do this but it is an incredible amount of work, and is in practice near impossible unless your police get involved, which they will not do unless it is a serious matter.

You would need to obtain court orders from each ISP or telephony provider you require information from, which may be in several different countries, which would require showing cause, i.e. that some sort of criminal offence or tort had occurred, and that it is reasonable for you to demand cooperation from them as a third party.

This will cost tens of thousands of dollars/euros/pounds at least. You may also be required to pay the ISP costs of complying with the order, in addition to the very high costs of lawyers who work in this area.

And all to find out that it was a random phisher.

On the other hand if you have suffered no harm, and you cannot show a crime was committed, you will not be able to get the court orders and ISP cooperation you need.