Seriously? Not one "you must be fun at parties" gag post? Ya'll slipping.
Your friend at the very least should introduce fringe friends to larger groups. It's how you get your friend groups to sorta get along and prevent your parties from becoming too cliquey.
But seriously, parties aren't terribly hard when you don't drink or don't care to dance. Grab a Solo cup, fill it with ice and diet coke, and walk over to where a drinking game is taking place. Watch for a while, comment on the proceedings to anyone who'd bother to listen. Go to the dance floor. Comment on the music to anyone who will bother to listen. Go to the kitchen where there might be a conversation taking place. Hang out on the fringe. Interject if you feel you can contribute. Make frequent trips to the snack table. Inquire about the maker/bringer of any particularly interesting foods. Go to the TV. Ask them to throw on *insert funny or interesting show _____*. Marvel as someone will inevitably go, "Hey, I love _____! Have you seen other _____?"
Once every 45 minutes or so, find your friend. Randomly insert yourself in whatever circle he's talking in. If he's not a complete weirdo, he'll introduce you. Be prepared to answer the easy questions. How do you know the friend? Where did you guys meet? How long are you in town for? What are you doing while you're here? How awesome/boring is your hometown? What do you do? Have any embarrassing stories about the friend?
Staying on your phone can make you look busy for short lapses, but if you're there for an hour, it just makes you look lonely and sad. And no one wants to talk to people who are lonely and sad.