I am not sure why so many parents think phones are so important and special and that children need unlimited acceas to learn to self regulate. Don't you limit/control other things? Like sweets, soft drinks, alcohol and crossing the road?
No, no limits, and they learned to regulate themselves. I discouraged alcohol, and the age limit to buy your own and be served in a bar or restaurant here is 21, but they were all off to university at 18.
If I wanted to limit sweets or soft drinks I wouldn't have bought them. I didn't in fact buy soft drinks regularly, and didn't model consumption of either soft drinks or sweets.
They had phones from the earliest time they were available (early 2000s) and watched as much TV as they wanted to, both in the sitting room and in their rooms. We had wii, various Play Stations and other platforms. I never got cable TV, but we had DVD players and lots of DVDs.
They also got to regulate their own social lives, with the condition that if their grades started slipping they would have to sit down and make a plan to ensure recovery. Kids learn to drive at 16 here, and if you haven't managed to transmit your values and priorities to them by then it's hard to do it after that, when their friends have cars and not all of their peers are as focused on getting into good universities as they are.
The same rule went for extra curricular activities - if the grades slipped or homework was being done at 3am regularly, then it was time to revisit the decision to do a sport or take part in the spring musical, or whatever.