This is a continuation of looking at people using their phones.
This is probably one of the "classic" ways in which we use our phones: while walking, we hold it to one of our ears. This gives quite a busy appearance as you are doing several things at the same time: walking, carrying things, talking and listening while still having to navigate in the world around you. It wouldn't be too surprising to see people's expression being similar to her face in such a situation, indicating an elevated level of stress or at least heightened concentration.
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