Yes, exactly this ... ^ I have my phone and DH has his ... I never look at his and he never looks at mine. We both have PINs on there to get into the phone (and also to access our laptops.) I don't know his for his phone OR his laptop, and he doesn't know mine.
I think it's very bizarre to go to your husband's phone to order pizza. I'm pretty sure most people have their own phone closer. It just seems like an excuse to look through his phone ... I don't want my husband looking through my phone - and although he hasn't said he wouldn't want me looking through his, I wouldn't anyway, as I don't want him looking through mine.
I have conversations on Whatsapp with my daughter, and 3 best friends that I wouldn't want my husband to look at. And sometimes I buy him gifts for Father's Day, wedding anniversary, birthday, Christmas etc, and I get Amazon and eBay notifications popping up - and it will give it away to him what I have got.
I have a diary, and I have three penfriends who I write to, and my diary and letters are all private as well. I wouldn't want him snooping through them either. My phone is private and part of it is like a diary to me ... (Whatsapp messages and normal messages.) Just because you're a married couple of 20 or 30 years, that doesn't mean you need each other's passcodes/PINs to your phones, so you can go snooping and mooching around in each other's phones.
It's just a bit weird to me. I know a marriage can't survive on lots of secrets, but there's no secrets between me and my husband. It's just privacy. (OK, maybe there's a few little trivial secrets, but everyone is entitled to those!)
I'd go absolutely crazy if I thought I couldn't have my privacy. As a previous poster said, I think couples who are supposedly 'transparent' and have everything open, and have each others passwords for everything - THEY are the ones that don't trust each other - because they seem desperate to be able to look at their partner's private stuff.
As another poster said, if your partner's going to have an affair, they'll have one whether you've got the passcodes to their phone or not. Some people would just use another phone, or message people on the laptop - keeping contact by email or something.