@RogueM OK a quick update.
I checked with the LE guys, and smbus is available under LibreElec (it's in the system tools addon). I've got that installed, plus written an add-on which includes your py files for touchphat and cat1xxx, plus I incorporated your button.py file as a test. The addon runs without generating any python errors in the log file, but the pHAT doesn't do anything.
The hardware is fine, as I checked it under a new Raspbian Lite install with your one-line set-up and after a reboot it worked as expected with the button.py test file.
If I get time I'll do more testing tonight, as I want to fully check that I2C is enabled (LE has an I2C tools add-on but I've not explored yet what it can offer) and whether I can get anything working via SSH directly outside Kodi. If it would be useful I'd be happy to send you the add-on plus instructions on what else LE may need adding to get you in the same set-up as I have.
One other question - does the touchphat require any specific dtoverlay settings in config.txt?