Incident searches are not about the safety of officers (this has come up on HN before). If you follow the cites and the doctrines, it turns out that incident searches have always been about collecting and preserving evidence as much as safety. I think incident searches get confused with Terry stops, which are solely meant to be about officer safety.

The unique issue at play in incident phone searches is the notion that a phone is a little like your house; that if you're arrested during (say) a traffic stop, the police don't have the authority to drive to your house and search it too. Similarly, if you're arrested at a traffic stop, getting access to your trunk can be legally iffy too; incident searches are restricted to your immediate vicinity.

This is something SCOTUS is going to resolve next year.