Why my IPhone 11 get heated after few minutes of using?

It would depend on what the few minutes of using you are doing. The iPhone will heat up in use, depending on the task. Processor intensive tasks, such as video calls, graphic intensive games, or weak cell signal will also contribute to heating. The phone will feel heat in the back near the camera area. The phone will also exhibit heating when the battery is charging. Since the iPhone does not have a fan, the heat is dissipated by the case of the phone. These are normal, so long as the heat does not get to the point to shutting the phone down after an overheating warning appears on the screen, or it seems way too hot to hold.