unresponsive iphone

so sometimes when my phone gets too hot it will start to lag and i have to restart it. but today i tried to restart it and it wouldn’t let me. so now my phone is not letting me turn it off and it won’t let me open any apps. i have no idea what to do. i’ve tried to force restart it and just turn it off but nothing is working. siri can’t even open my apps for me. everything is unresponsive except my power buttons. it lets me hold down the power button ana activate siri but when i try to hold down the power button and the volume buttons nothing works.