Hi @oneteaspoon; happy Monday!
I'm sorry to hear about the issues you're having when using the mobile app on your iPhone.
If you've already ensured your device's OS and our mobile app's version are up to date, I'd suggest reinstalling the app as this might do the trick here.
Before you get to that though, you may want to try clearing the app's cache first. Here's how:
1. Navigate to the “Personal” or "Account" tab
2. Tap the gear icon in the upper-left corner of the screen
3. Select “Clear Cache”
Once this is done then please ensure you log out of the Dropbox application, then restart your device and log back in again.
From there, try scanning a large file anew and let me know if the app crashes again.
Thanks a bunch!