A one-second phone check rarely costs one second. Getting your focus back is the expensive part.

Attention does not switch cleanly. The glance costs a second, but gathering your thoughts back up costs minutes you never budget for, and you rarely feel the loss because no clock shows it. Thirty quick checks across an evening can eat an hour of real thinking. That is how a two-hour session produces twenty minutes of work.

Time one session honestly. Put the phone face down in another room, work until a natural stopping point, and see how much further you get than usual. If going without it feels uncomfortable, that discomfort is itself the measurement.