The battery will naturally warm up whilst charging but your phone should never get too warm to not be able to handle it.
I assume your using an official charging brick.
Also if the phone has a case and or screen protector this can hinder heat dissipation.
If your concerned then a Samsung Experience Store or Samsung Service Centre can run a diagnostic test on the phone.
Daily Driver > Samsung Galaxy s²⁵ Ultra 512Gb ~ Titanium Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
