More common associated risk: Police detain you and point your phone at your face to unlock it (or unlock your access to some other resource).

That is not a very high-tech or high-effort attack and could be relevant if you're concerned about the police.

Someone might say that this concern is useless because the police can also coerce you to unlock your phone via a different method, but that depends on the law and culture in your particular environment (I guess ranging from "extremely unlikely" to "almost certain" depending on where you are).

Edit: I don't mean to disagree with your overall point that understanding the threat landscape and threat model is very important, just to say that there is a very simple and plausible threat to which the precaution you used as an example can be relevant.