Bosses and managers must definitely lead by example.  It is all about 'monkey see, monkey do'. During the day, they must take into consideration on how much time they spend on their smartphones.

To avoid problems of unnecessary phone usage, senior management should take the time to clearly define and communicate company rules of using their mobile devices during working hours. 

Another way could be letting employees go (at times) - allow them to take a short walk or breaks which could boost productivity and creativity. If you notice employees playing games mid-day, encourage them to take lunch breaks with their colleagues to aid on team bonding and reduce the use of their smartphones.