In my experience, there is usually an obvious difference between seeing a phone used as a camera versus not, based on whether it's aimed at an interesting subject or not. There are exceptions, like sitting with your elbow propped on the arm of a chair for a few minutes to avoid fatigue, which causes the phone to be at eye level and therefore perfectly vertical, but this is rare.
In my experience, there is usually an obvious difference between seeing a phone used as a camera versus not, based on whether it's aimed at an interesting subject or not. There are exceptions, like sitting with your elbow propped on the arm of a chair for a few minutes to avoid fatigue, which causes the phone to be at eye level and therefore perfectly vertical, but this is rare.