Might not apply to you then, but I found this:
“Your iPhone might get slightly warmer while it charges. To extend the lifespan of your battery, if the battery gets too warm, software might limit charging above 80 percent. Your iPhone will charge again when the temperature drops. Try moving your iPhone and charger to a cooler location.”
I’m using a 2A plug on a cheap wireless pad, and the phone is charging to 100%. The plug that comes with the phone is only 1A.