Assuming that's true*, it honestly isn't good reason to give your kids a smartphone. Your job description as a parent is pretty much to stop your kids from doing things they don't understand will hurt them. There's (imo) plenty of evidence that smartphones are hurting kids, and therefore it's a parent's job to crack down on it even if it costs them in their social life. Like, if all the other kids were shooting up heroin it would be considered insane to say "you have to let them do it because all their friends are junkies", and I don't see it as being different for phones.

*It's also not clear that your premise is even true. Plenty of parents in the past have reported how their kids' friends adjusted just fine to not being able to use a smartphone to contact them, and that they still had healthy social lives.