I'd be very surprised if a smartphone, syncing itself to a reference, is ignoring seconds. Why would it?
To me, if a clock that doesn't display seconds is displaying 09:30, then I assume the time could be anywhere between 09:30:00 and 09:30:59.
Presumably when setting the time on a device that doesn't display seconds, the seconds are being reset to 0 (i.e. setting time to 09:30 is setting it to 09:30:00), so if someone really cares about sub-minute accuracy they can take this into account.
To me, if a clock that doesn't display seconds is displaying 09:30, then I assume the time could be anywhere between 09:30:00 and 09:30:59.
Presumably when setting the time on a device that doesn't display seconds, the seconds are being reset to 0 (i.e. setting time to 09:30 is setting it to 09:30:00), so if someone really cares about sub-minute accuracy they can take this into account.