No pouch policy. Younger years aren’t meant to use them in school (8.30-4.00) - they should stay in bags. My dd does that, but there are some DC who have TikTok, full internet access etc enabled on their phones and do use them during the school day. The school laptop is well locked down (they do it by age range) and has very sensible net nanny controls which you can change to some extent if you wish.
Older years have gradually more freedom. It seems to work well for my older dd - she uses her phone to listen to background music through a headphone, if the teacher allows it in class during quiet working, for instance. If you want, you can see the whole policy - spgs.org/wp-content/uploads/2023/03/Mobile-phone.pdf
In terms of controls on WhatsApp, you can limit the times it works (so it won’t ping all night) and also google how to set the privacy settings for maximum privacy. Unfortunately your dd could change them, there’s no way to stop her doing so. I agree WhatsApp is not the app that most teens use, but I think the privacy, security and safeguarding concerns around things like Snapchat and TikTok are significant and haven’t allowed those yet. It’s an ongoing conversation.