I've gotten plenty of "why" answers in these forums from very knowledgable users in the past (which is why I asked this time). Out of curiosity, I turned to ChatGPT and this is what it said (with verified source links). Including this here for future seekers to find!
What you’re seeing when your iPhone shows very low free space at first (e.g., 11 GB) and then quickly jumps to a much higher value (e.g., 126 GB) in Finder on your Mac is a common behavior, and here’s why it happens:
💡 What’s Happening Behind the Scenes
1. Initial Estimate = Cached or Stale Info
When you first connect your iPhone to the Mac and open Finder:
- macOS pulls a quick initial status from the iPhone.
- This status might be cached from the last session or pulled from a quick estimate that doesn’t yet account for temporary data cleanup.
Think of it as a “first glance” that hasn’t had time to recalculate space properly.
2. Storage Recalculation
Within a few seconds:
- The iPhone performs a deeper internal cleanup and storage scan.
- It may remove or offload temporary files, Safari caches, system data, or log files.
The true available space is recalculated and sent back to Finder. That’s when you see the jump — from something like 11 GB to 126 GB.
🧠 Why Does This Happen?
- iOS dynamically manages storage, including system caches and temporary app data.
- These “System Data” and “Other” categories can temporarily balloon, especially if the device has been running for a while without a restart or backup.
- When you initiate a backup, iOS prepares the storage, clears caches, and frees up space that was never really “used” in a permanent way.
✅ Is This Normal?
Yes. This is a known and normal behavior for iOS devices — especially before a backup or sync operation. It’s similar to how macOS shows disk usage estimates during cleanup or software installation.
