Iphone frozen while iOS update installation

Try a forced restart and see if that lets you get back into the phone and continue with the update.

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.

If you don’t have a computer, you might not be able to fix this. Based on what I see on your phone screen, you should try putting the phone into recovery mode and then try updating it that way. If that fails, you maybe have to restore it. If you have to restore it, you can restore a backup to recover your data, if you have one.

See the instructions in here.

If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support

If you don’t have a computer, you can ask a friend or family member if you can use their’s or make an Appointment at an Apple Store and ask for their help.