For phones, though, the absolute amount of energy is so low that a high percentage loss doesn't actually mean that much. A typical smartphone battery is about 15 Wh, so charging it literally every day for a year consumes 5.4 kWh. Doubling that won't make a noticeable difference to your energy consumption, the heat released in your home, your electric bill, etc.
That's why small device chargers are engineered without much regard for efficiency. For that specific application, having long flexible light cables is better than making sure it squeezes every bit of efficiency out of it.
For cars, though, even a 10% loss can make a difference.