It’s not okay, ever imo. To me my partner going through my phone either means they’re insanely insecure, don’t trust me, are projecting their mistrust or all of the above. Can they use my phone to order food or call/text someone if their phone is dead? Yes. But going through my texts/social media dms etc? Complete violation of my privacy. That being said I have nothing to hide, ever so if they ask then yeah sure, but it’ll also completely change my view of them.