1) Will it continue to be legal?
2) Do I care about ethical concerns and does something being legal make it ethical?
Other people who are in a different position from you will be exploring this to determine if #1 should be changed.
You're just perpetuating the prejudice of minorities, even if your coming from a good place.
People with higher incomes probably buy more expensive phones. You already have their income on a loan application, so you don't need a blackbox NN model to confirm it.
Throwing in a bunch of corrolated features into a model won't help improve accuracy.
But if you throw in a bunch of weak features that together sum to a predictor of race (or other protected attributes), then aside from being grossly unethical, may well be illegal.
Contextually there is no reason to suspect that a phone operating system has anything to do with anyone's ability to repay a loan, anymore than the color of their car or their eye color.
Income and existing debt does, obviously.
What you don't want, and what is not legal, is denying a loan because of nonsense predictors that happen to be very strongly corrolated to race and very weakly corrolated to the ability to repay a loan.
If color of car, or operating system, is a strong predictor then the model is probably being overtrained on the training data and probably wouldn't generalise well in the real world.