Social media and personal technology can both make our world better and make our world worse. Teens tend to understand this more keenly than adults.
Depending on the ages and maturity level of your teens, you can either lay down ground rules for the sessions (e.g. everyone turns off their phones and puts them on the table, face down) or have a discussion about what is an appropriate use of technology in small group sessions.
There is no exactly right or wrong answer here, but it is worth considering how much time teens spend on their phones, and how powerful face-to-face conversations about real issues like faith, life, and God can be. Whatever you decide, be clear with the teens about the rules or agreement, and hold them accountable.