How can I see the number WhatsApp is dialing instead of the name? How can I see the number WhatsApp is dialing instead of the name?

My friend Erwin has two mobile phones, one in Switzerland and a new one in Vietnam. Yesterday he called me from Vietnam by WhatsApp. Simple-minded as I am, I added this number under the same contact "Erwin". Today I wanted to call him back by replying his last WhatsApp call from yesterday (I selected his WhatsApp call from the call protocol). However, WhatsApp obviously connected to his Swiss number (as he's registered there as WhatsApp user), and nobody picked up, of course, because it was switched off. In such cases it would be very helpful to see the number WhatsApp is using. How can I make this number visible?
You can't make the number visible, as the developers of the Whatsapp hasn't add that functionality.

You can however check after the call


  Go to CALLS tab -> Select the Contact -> click on Message icon ->
  Select the View Contact from Menu -> About and Phone Number will show
  the Contact number