In this video, you will realize that the office app works in both landscape and portrait, with the hamburger button is used for navigation in the top left. You will see it’s very similar with using on a PC.
In the video you can also see a walkthrough of other new features including some modifications to the way you change the images on the Start screen. It also shows off Spartan in this build but it does not look like there are many significant changes.
The redesigned Store is also of interest here, and this new UI is part of the company’s efforts to offer a unified apps repository across all devices. No indication that these are the very features that will be rolled out to users, and a lot can change between now and when Windows 10 for Phones officially sees daylight. But so far so good. More information is likely to be provided at BUILD 2015 later this month, though.
Some more images of Windows 10 for phones build 12544 shown off: