Why is my phone screen unresponsive?

Recently, i was at a swim meet. (and no, NO water touched my phone.) I left my phone out on the chair directly in contact with the sunlight (and it was pretty hot.) when i first picked it up, the screen was extremely laggy and slow to respond because of how hot it was. but then, i started to notice even when it cooled down that the phone screen was unresponsive. sometimes when im using it, it randomly just stops working and i have to wait about 30 seconds for it to start working again. its been 2 days, any ideas how i can fix this?