iPhone 11 keeps resetting

I don't know if I can properly explain it but I'll try. So basically every now and then my phone would close apps, and reset like when it dies except it just goes back to the lock screen. I've been able to solve this by deleting some videos or apps. However now my phone is in this cycle where it does the reset thing for about a minute, then it shuts down. Then the white apple logo comes up for another minute. After this, it takes me to my lock screen where I can't do anything except enter my password. After I put in my password it takes me back to the reset thing and the cycle start again. I've tried holding down the sound and power buttons to hard reset and nothing, I've left it for a couple hours and again nothing. I can't back it up because I can't unlock the phone. If anyone has any ideas please let me know.

Thanks