Parent 1 is wrong. It isn't about trust, it's about safeguarding, and all parental advice is that you should check your child's phone and limit access/followers etc.
DD's first phone was a Monqui that I got on a free trial on MN. It was great as I had to approve all apps and add contacts and it tracked her. She was around 10 at the time. She now has a cheap iphone with a £10 sim.
I know of a local case that went to court where a 12yo girl was groomed by a 21yo man. He ended up on the sex offenders register and the girl went through hell. Her parents found out when they checked her phone usage and were horrified to find obscene messages and photos.
DD has a friend, 13yo, who will stay up til 3am editing stuff on her phone. Her parents only discovered that when they checked her phone usage after she was tired all the time.
I don't read DD's messages with her friends, but I do check who she is following and who follows her. She has had messages from older men.
There are girls in her year, 13yo and posing in their underwear asking for "likes" and ratings by boys. Their parents don't know as they never check their phones. I do not want my daughter doing that.
Any sensible parent would check the phone's content every now and then and also have "Find my iphone" or similar enabled so that you can track them if you need to when they are away from home.
This link has lots of useful advice:
www.internetmatters.org/