Diagnosis
Yeah, this one's common. It's not 'normal' in a good way, but it's a known thermal management quirk. The processor can get warm during background tasks like indexing your music library or processing Siri requests.
How to Fix It
First, check its location. Is it in a tight space, on a shelf with other warm electronics, or in direct sunlight? Move it to an open, well-ventilated spot with at least a few inches of clearance all around. Also, try a simple restart (unplug for 10 seconds). This can stop any runaway background process.
If That Didn't Work
If it's consistently too hot to comfortably keep your hand on, there might be a hardware fault. Check for any recent software updates on your iPhone, as Apple has released updates to address thermal performance. If it's still bad and under warranty, contact Apple Support.
Heads Up
Don't put anything on top of it, ever. The fabric cover traps heat, and blocking the top vent is a surefire way to make the problem worse and potentially shorten its life.