This seems to be a bold statement for an article that boils down to:

"iPhone is connected to a charger, it gets warm -- warmer than if it isn't connected, and even though that increase might only be a few degrees above room temperature, doing this overnight, every night, doesn't seem smart to me."

A significant amount of wrong and misleading things in this article

> decided to do some experimenting to find out.

Proceeds to do zero experimenting.

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If one is so obsessed, just use a 5W charger, it'll practically (with the overhead of the phone running) take the full 8 hours to charge, with all heat being dissipated before it can cause any damage