What app is this? Is one provided by your carrier or the service you're using for VM?
What happens if you just touch the grey area that says the name of the caller?
What happens if you touch the avatar/image placeholder?
Where is it getting the name for the caller? Have you already saved them to your contacts and given them a name?
What happens if you begin dialing the name on your dialer? 26677 (COMPR) usually brings up previous calls and contacts that match and you should be able to see the number that way.
Welcome to Android Central! Typically, as VidJunky asked about, you have to tap the profile pic (in this case, the image placeholder) to see those details.