I would focus on what you can control. I think you could politely mention that you think they are on the phone too much and you feel it is an unhealthy habit. I would say that's about the most I would intervene. It gets them thinking about the amount of time they are on the phone/internet and leaves it in their hands to make a change.

Anything more than that will be seen as pushy and overstepping, which will just give them a reason to dismiss you. The main thing I'll say here is that it's not your responsibility to "save" the people you care about in your life. The biggest impact you can have is focusing on yourself and setting a positive example for those around you.