My phone will not power off ,I pressed two buttons and still is not working

try this to do a normal power off and back on

Restart your iPhone - Apple Support

Should also be able to go to Settings > General > Shutdown

to do a force restart

• iPhone 8 or later: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Side button until you see the Apple logo.
• iPhone 7, iPhone 7 Plus: Press and hold both the Top (or Side) button and the Volume Down buttons until you see the Apple logo.
• iPhone 6s or earlier: Press and hold both the Home and the Top (or Side) buttons until you see the Apple logo.