Problem charging iphone 6s

I have a problem charging my iphone 6s.

I plugge it to the charger and battery percentage doesnt go up. But icon of charging apears.

Then i unplugge the charger from the phone and plugg it again and percentage start going up But really fast úntil it gets to an X percentage and then it continues charging normaly.

What should o do in afraid this Will distroy my battery.thanks.