Grapi
This is true that charging with a lower current preserves the battery from extra heat, but I think for modern phones using a 5W charger is better when the phone is completely idle or even turned off.
I noticed some power-intensive operations on today's powerful phones take above 2A, which the traditional 5W charger can't deliver.
So, if you put your phone on 5W and then keep using it, or any power-hungry app/automation keeps draining more than the current that the 5W charger can deliver - it's actually worse for the battery, switching between charge/discharge cycles so often.
Common scenario - gaming when the phone is charging. This put even more heat or happens the above-described.