This paper by Miluzzo, et al. speaks of the "low-level context" of the mobile device:
We believe efficiently computing the low level context of the phone,
that is, the position of the phone carried by a person (e.g., in the
pocket, in the hand, inside a backpack, on the hip, arm mounted, etc.)
in relation to the event being sensed -- which we call the phone
sensing context -- is a fundamental building block for new distributed
sensing applications built on mobile phones.
This paper from Ubicomp uses the word placements, as well as placement contexts:
In this demonstration paper, we show a novel approach to detect the
common placements of a mobile phone, such as “in pocket”, “in bag” or
“out of pocket or bag”, from embedded proximity (IR) and light
sensors. We use sensor data fusion and pattern recognition to extract
distinct features from sensor signals and classify the boundaries
among these three phone placement contexts.
You can follow suit, e.g. Accurately Determining Mobile Device Placement Contexts Using...