Earlier quoted context omitted.
navigation/gps? workout app? whats the difference between a workout app on my iphone compared to a dedicated device (e.g. garmin edge) in terms of safety?
You shouldn't be actively using, interacting with, and providing manual input to your device (be it a phone, garmin edge, or anything else) while cycling. An occasional glance at a navigation app (on a screen that is held by something other than your hand - a clip, stand, etc.) is probably fine - but taking your hand off a handlebar long enough to hold a device, and taking your concentration off your path long enough…
a) the shaking feature turns on even if i don't type anything just by the virtue of the phone being active (shaking can mean 'undo', not just 'undo typing')
b) i have it mounted on a quadlock on my handle bar, no holding whatsoever.
c) i take the risk of asking for trouble while cycling on a cycling path with no other cyclists near me (within, say, 300m). I am not cycling between 2 double decker buses while texting...