Touchscreen on Iphone 11 pro max goes weird and is sometimes unresponsive

Just brought this phone and it seems that when I message strange things start to happen. Keys and letters are submitted that have not even been pressed. The phone is also sometimes very unresponsive.. I have reset the phone and everything worked for a while BUT the issue returned. I am going to delete my backups and reset the phone again and hopefully this will work fingers crossed. What should I try if it doesn't?