Not to knock the original post in any way as it is clever...
Here is an even better way... check the instructions for the details.
https://www.thingiverse.com/thing:4579946
https://www.ecstuning.com/b-inbay-pa.../240000-03~iby
Remember in both cases that you'll need to keep cards and other objects away from the charger as they will be demagnetized by the charger.
The electronics provided in the link above, hook directly to the exiting car wiring and do not require the USB connection.
The electronics could also be used in place of how the OP did it as well.