At this time, you can only choose a Tablet or Phone Layout for your App. There is no way to determine the device you are on accurately in order to adjust.
You would have to start with the largest format of Tablet Layout to cover both types of devices with one App. Tablet Layout Apps appear in landscape mode on a phone (really not so bad of an experience for the user). If you could determine the device type, you could do some wild control placing in order to adjust, but you'd still be in landscape mode on a phone.
I would simply say this - with all the work you'd have to do to adjust in formulas all of your controls for a different layout - you are better off just having 2 apps, a Table and Phone layout.
Hope this gives some help.
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Like Randy says, you have to pick one or the other. However, there was some talk here a while back (I think) about a single app being able to accommodate both formats (portrait vs. landscape). If you wanted to build toward that future ideal, look at Parent.Width and or Screen.Width. You can render the sizes of controls, their position, and their visibility dynamically... either based on each other or on some fixed point, and you can drive your figures based on the width figure.