LOOK UP!
Stop giving the ground or the cellphone all of your attention when someone is approaching. Look up and see who's around you.
To this day, I will not trust someone who will not look me in the eyes, give me a firm handshake, &/or acknowledge my presence.
Everyone wants to be seen, but few care to see anyone else. Just a basic courtesy of acknowledging somebody else's presence with a smile and a nod can make their day (and yours when they smile back). That moment of acknowledgement can give you (and them) an affirmative reminder that none of us are alone in the world.