Samsung phone won't charge and brings up temperature symbol

The other day I tried to charge my phone, but the battery symbol would turn blank and start blinking, refusing to charge. Eventually the phone ran out of battery and while plugged in, would display a yellow triangle with a red thermometer symbol, I assumed that it had a temperature issue and so left it for a few hours to cool down.

When I came back and tried again, I got the same symbol, and still I haven't been able to charge my phone. I wouldn't mind too much, but I just got a new phone and I need access to my old one for some things to sync. My phone is a Samsung Galaxy S9+