As someone who used to have to deal with these terms on an official CAA form - and how users interpreted them, my experience suggests that:

Take off - any point from push back to start of descent
Climb out - any point from start of take off roll until landing
Approach - any point from start of descent until connection of the air bridge/arrival on stand
Landing - any point from start of descent until the flight crew arrive home

Ok, maybe I exaggerate a little

I would not be suprised if in some locales (i.e. LATTC), 'approach' is area radar -> local control, landing is local control and take off is until the point you hand over to area radar. Of course, as a pax you might not have any idea when that occurs.

As a rule of thumb we developed, approach was anything greater than 2000 ft (= 8 mile finals on a 3o glidepath), landing was anything less than 2000 ft, take off anything up to 2000 ft and climb out was anything more than 2000 ft.

And yes, many countries do have speed restrictions below 10000 ft - there were some trials in the US (HOU IIRC) to abolish this, but Canada did a very good safety analysis, pointing out the vastly increased risk, set against theoretical/marginal benefits at best...

As for the practicalities of electronic use - I usually use the seat belt sign as well, unless it appears the seat belt sign is being kept on for other reasons.