Have older LG smartphone - touch screen no longer accepts 'touch' - cannot make or answer calls... ideas?

If the touch screen of your phone cannot work without experiencing any physical damage, it is probably caused by software issues. In this case, there are several means you can try to fix the issue.

1. Restart the device

When an error occurs on your phone, the most direct but simplest way to settle the problem is restarting the device. That's because this means can stop all the running applications on your phone which can release the device from heavy load. And the operation is very easy- press down the Power button until the screen gets dark. Then wait a minute and hold down the Power button once again to start the phone.
This way can turn your phone back to normal status at most time.

2. Take out SD card & SIM card
Sometimes the SD card or SIM card on your phone would cause some issues as well. Thus, you can try to:
Turn off the mobile phone and then remove the back cover of the device to take out the memory and SIM card.
After that, you can reboot the device and check if the screen is responsive now.

3. Inspect whether there is malware or incompatible application on your phone
Malware or incompatible applications on your phone could affect the phone running as well. Hence, you can boot your phone into Safe mode to see if it runs well in this mode. If it does, you need to delete or uninstall the programs that you have installed on the device recently. Here, to enter the Safe mode on Android phone, you have 2 means:
Switch off the Android phone and long press the Power button to reboot the phone. Then release the Power button when you see the brand logo of your phone. But immediately, you need to press and hold the Volume Down button until you see a Safe mode indicator at the bottom left corner.
Press down the Power button until an options menu shows up. Just long press the Power off option and you will gain a message asks you whether to reboot the device into Safe mode. Just tap on OK.

4. Factory reset Android phone
No matter what kind of Android problems you meet, the most mighty and effective way to settle the issue is to factory reset the device. But meanwhile, it is also your last option since it would erase all the settings and data on your phone. Thus, before performing the resetting process, you'd better backup the wanted files on your Android phone in advance. Then you can:Boot your phone into Recovery mode.
https://www.mobikin.com/android-recovery/fix-touch-screen-not-working-on-android.html

To enable USB debugging on Android with a broken or cracked screen, the most effective way is to buy an OTG adapter and a USB mouse, which enables you to perform your phone with the mouse. But please make sure your Android phone is compatible with OTG adapter.
Step 1. Connect your Android phone to the USB mouse with the OTG adapter.
Step 2. Enter the password to unlock your Android phone using the mouse.
Step 3. To enable USB debugging mode on Android, please go to "Settings" > "Developer options" > "USB debugging".
(If you can't see USB debugging, please go to "Settings" > "About device" > tap "Build number" for 7 times > "Developer options" > "USB debugging". )
Step 4. Connect your Android phone to computer with a USB cable, and the computer will automatically detect your device now.
Step 5. On computer, you might select the files from Android to transfer to computer easily now.

Tutorial to Turn On USB Debugging on Broken Android

Damaged screen --need to replace