Default powerbank 2A output bad for phone ?

What's the side effect of using 2A output powerbank on the cellphone ?
From my experience, the output of cellphone adaptor usually between 500mAh-1Ah. Well, except phone with bigger screen (which i don't have).

What i notice is, the back of the phone are usually hotter compare if i charge my phone using phone adaptor or via usb.
I am kinda worry with this excess heat. Heat is not good for electric components.