iPhone screen frozen

Hi,

this afternoon my iPhone screen froze mid-use. it is stuck between tabs. the touch screen still works and the buttons still works however I cannot move from this screen. I have asked siri to close or open apps and it can't. I am still receiving messages on my home screen. I cannot switch the phone off. I have tried to update as one is due but I do not have enough storage and can't sort anything while locked out.

Can you advise what I should do

Many thanks, Grace