Skype has just been updated to give users the option of selecting a "classic" UI instead of the new and improved tablet interface. The previous update to Skype added many new features and a more tablet-optimized interface overall, including a portrait UI for calling -- the curious part was the rest of the app was still locked in landscape mode. Skype is now backpedaling, sort of, by letting tablet users go back to a phone-style UI in the settings if they prefer. The new option is probably a better choice if you're on a smaller screen like the Nexus 7 that is often used in portrait.
10-inch tablet users are still better off with the new "tablet" UI because the larger devices are quite comical in portrait mode. Until Skype figures out how to do a responsive tablet UI that changes appropriately for landscape and portrait use, it's good to have this option. You can grab the update from the Play Store link at the top of this post.