It could cause the opposite effect with people being annoyed at another parent trying to dictate the way they parent, even if they weren't planning on getting a phone just yet.
It will also then alienate the ones who have already given their child a phone - you say some have.
I think you do what's right for your child and let other parents decide for themselves.
Dd got a phone in test 6 - it seemed to be the birthday present of choice as the children turned 11y, with some with later birthdays getting one at Christmas instead. Some got them in the summer holiday before year 6, in preparation for walking on their own.
And many didn't get new phones. Often it was a parents older phone - maybe a couple of years old so still a good quality smartphone just hit the latest model. So they wouldn't have wanted to be time it should only be a basic phone - for many it's cheaper to have a cycle of passing in an older parent's phone than buy by an alternative. Plus many like the parental control features in a smartphone,, as well as apps like 'find my iPhone' and being able to link accounts more easily if all same make.
Fwiw Dd had a phone at age 11. She's now 21 and we've had no issues from phone and app use. We were very strict with no phones at bedtime, phones left charging downstairs, having full access to the phone and all apps and passwords, but being able to download even free apps without permission (had to be password approved by a parent on their phone) and very restricted when it came to social media for the first years. We went down a supervised, regulated approach with lots of online safety guidance at home.