Hi @helenr,
First try starting the phone in [https://support.t-mobile.com/docs/DOC-30290|safe mode] and check if the touchscreen works, If it does then a downloaded app is the cause of the problem. The trick is to find out which one.
If it doesn’t work in safe mode either then there is a problem with the touchscreen either a loose connection to the systemboard or it is faulty and will have to be replaced.
Here’s a link to the ifixit [guide|110387] guide, which may be of some help.
Before you open the phone to check the touchscreen cable or to replace the screen, try connecting a USB mouse via an [https://www.amazon.com/Micro-USB-Data-Transfer-connecting-compatible-Accessory/dp/B01MFE8T7J|OTG cable -example only] to navigate through the phone so that you can send the pictures by email to your computer.
Make sure that the phone’s battery is fully charged before you do this, as the power for the USB mouse is supplied by the phone’s battery and it will discharge quicker than usual
If you have a pattern lock on the screen, unfortunately this method won’t work.