If it’s a zombie apocalypse, then I would assume the grid is down. Critics would say that the battery and the durability is a problem, but I don’t think it’s a problem in this time and age. So is the phone really the best source of knowledge during a zombie apocalypse?
As far as collecting immediately useful intelligence of zombie movements, I think a foxhole radio would be more maintainable than a cellular phone.
spoiler
If you’re lucky, you can find a ham radio operator with such a device. You could use the radio to coordinate with other distant groups who may have resources like the smartphones you are referencing. Yes, smartphones are technically radios, but I donʼt think the required cellular towers can be relied upon during an infrastructure collapse.
A commercial handheld radio would be more efficient, more capable and easier to use than one built with scraps. Still, you cannott download offline maps on a radio