Your brain can't handle walking and using your phone at the same time — so look up.

Safety adviser Murali Krishnan points out that walking and using your phone both demand large amounts of cognitive effort. 

As a result, you can't fully focus on both at the same time in the same way you can with walking and gum-chewing, for instance. You'll suffer "inattention blindness," where you may see an object but not process that it's a car speeding toward you.