Why won't Iphone XR won't turn on?

Why won't my iphone XR turn on? Or how can I turn it on? My Iphone won't turn on unless connected to a charging port, but when connected, the apple symbol appears for about 5 seconds, then disappears, about 10 seconds after that, the dead battery symbol appears for about 5 seconds and disappears as well (Iphone has been charged), this process repeats until the IPhone is disconnected from the charging port, after disconnected the Iphone does not turn on at all. I am not curently using this phone, and it has been doing this for about a year now. How can I fix this problem, or what should I do? Please help. Thank you.