Talk to the person in front of you.

"Duh", right?  But how many people do you know that will spend their time at a party or an event or even a dinner table pecking away at a smartphone?  Here's what's wrong with that:
  1. Your interactions will remain superficial.  Nobody will open up to someone who's half ignoring them.  You will never make a close friend this way.
  2. You insult those who took the trouble to physically show up and spend time with you.
  3. You train people to use the phone to contact you, which in the future will both interrupt you and trivialize your interactions with them.
Give your undivided attention or stay home.  The former if you want to be human - the latter if you want to be alone with your phone.