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Here comes a triple threat! You can set up your mockup in not 1, not 2 but 3 iPhone 5s. The first two are set in portrait mode, the first one is white the second is grey on the top left of the stage. The third iPhone 5s is set in landscape mode below the first two phones. They all are set for an image of 640x1136px on a smooth concrete slab.
Drag & drop not supported, but you can still upload via this input field: