I would agree with you, but the danger of cellphone searches seems to be that smartphones allow access to data far beyond what they actually contain since they'

I would agree with you, but the danger of cellphone searches seems to be that smartphones allow access to data far beyond what they actually contain since they're often linked to numerous online accounts. Arresting someone doesn't give the police the right to search their email, but having access to their cellphone might give them the ability to do so. Allowing warrantless cellphone searches after an arrest seems at least somewhat legally reasonable to me, as long as police are limited to searching things physically on the phone.