You don't need orientation handling if you've cut all the other signals, so...
Power negotiation is also not a big problem. Just use a correct resistor on the CC pin and you can make the phone use up to 5V/3A, which is plenty for any smartphone. You'd have to make sure to use a 5V/15W capable power source, though.
I actually learnt a lot from these comments, so my thanks - USB-C is still just a mirrage on the horizion for me, so not something I have considered deeply.
Power negotiation is also not a big problem. Just use a correct resistor on the CC pin and you can make the phone use up to 5V/3A, which is plenty for any smartphone. You'd have to make sure to use a 5V/15W capable power source, though.