Depends what you do on them. If it’s only to be reachable, then the only thing the carrier and 3-letters agencies can gather is your approximate position, what you say on the phone line and what you sent in text messages. Don’t say anything personal and sensitive, and they won’t have much to gather in the first place.
They don’t get the troves of info they can sucks from all the mobile apps, etc, which is way more than they could with dumb phones.