One of the problems with this is that it is trivial to evade for someone intent on serious wrongdoing. A person who manufactures child porn for money, for example probably won't use their phone to transport it across a border. They'll transfer it over the internet, most likely in a surveillance-resistant manner.

Instead, these kinds of searches catch people who don't know they're doing something illegal, or who the government finds undesirable due to their associations or business activities that are legal in their home jurisdiction. They may also be used to map out networks of contacts.

I do not want governments doing the things in the second paragraph.