Firstly thank you making it clear that your location is not in the UK, and that some of your comments are based on your local experience rather than the UK.
I am currently reviewing in some detail the economics of pay per mile for my own PHEV. I agree that for some PHEV's depending on their use case, may be disadvantaged by the proposed UK system. But its complicated to resolve the process because the dino fuel economy can vary so much depending on the level of charge in the high voltage battery and the drivers selection of driving mode, their style of driving and the road conditions.
If you can complete all your PHEV journeys on electric only power, then the UK system of pay per mile of 1.5p will be advantageous, but as soon as you start to use dino juice, that benefit is depleted and and ultimately you are into the realms of double taxation becasue of the pay per mile and the fuel duty which based on a vehicle that manages 45mpg is 5.29 ppm + the electric 1.5ppm making 6.79pmm.
But it isn't that simple becasue with my own VW PHEV even when the battery is apparently depleted, it still retains some energy to operate the stop start system, and the hybrid technology still regenerates some energy from braking, and engine idling and pays it back when accelerating, so its a very muddy picture to actually establish the true cost per mile and the actual amount of energy used.