A government is there to provide certain important things that everybody in the country needs. A legal system, a police force, etc. And it needs money to provide these things, which is what taxes are for.
So the government needs to take some money out of the system, and the only question is where to take it from. The most important things like drinking water, basic food, essential medicines, etc. should not be taxed. Ideally everybody has abundant access to these things, so taxing them and making them harder to obtain goes against that.
On the other end of the spectrum there are things such as owning a collection of expensive cars, $1k bottles of champagne, 3 vacation homes, etc. It's not that it wouldn't be cool if everybody could have these, but the economic resources spent on creating things like that are for now probably better spent on things like improving health care, improving education, or making sure everybody has at least 1 roof over their head. So in my opinion it makes sense to first and foremost tax this kind of consumption.
The result is similar to taxing high net worth and high income, in that people who can't afford to consume much will be better off by taking from well-off people, but it no longer incorrectly taxes every rich person as much, even if their wealth is actually mostly spent on philanthropy. Taxing high income and high net worth people who would've given most of their money to charity, is the same as taxing charity.
Regarding taxing the iPhone more heavily, the fact that an iPhone is relatively cheap doesn't matter. A hundred dollars isn't that much, but if it's spent on a freaking golden milkshake, I'd tax the hell out of that. Nobody needs a $100 golden milkshake, and the economic resources spent on that $100 golden milkshake would've been better spent on creating twenty $5 nutritious meals. An iPhone is a less extreme example, and maybe better compared to something like a $30 burger. Nothing wrong with people having $30 burgers, but it makes sense to tax the consumption of a $30 burger, which is not something anybody really needs, more heavily than the consumption of a $5 burger, which fits more in the category of essential food.
The cheapest new iPhone in the US is $229. Adding $100 to the price is pretty steep.
I'm not arguing against the government collecting taxes. Nor am I arguing against taxing the rich. Taxing luxuries sounds like a way to extract money out of rich people, but the richest people are not buying all that many luxuries. When there was a luxury tax the wealthiest people figured out how to get around it as much as possible and it became more a tax on the posers than the rich. (Not that taking posers down a peg isn't a good idea too, but that's a different argument.)
The wealth taxes proposed by Bernie Sanders and Elizabeth Warren are aimed to actually extract money from the super wealthy, but it has been tried in other countries and completely failed and it would require changing not just US law, but changing the constitution, which is essentially impossible in the current political climate.
Wealth that is sitting in one place and not moving in any way (tied up in some sort of investment or multiple investments) is pretty much impossible for governments to tax without a wealth tax. Governments can tax income and in the US the top federal income tax bracket was over 90% for a while after WW II. Reagan got elected with an outcry against the remains of those taxes in the late 70s. We have long since gone too far the other way.
My proposal is to get the wealthy to move their money around changing their investments. The wealthy that Sanders and Warren really want to punish are the sleaze bags who compiled a mountain of wealth playing financial games rather than creating anything. Changing how capital gains (money made from investments) are taxed could incentivize some types of investments and make some very expensive to invest in. That will incentivize these money people to chase the lower tax options and end up pumping money into investments that end up benefiting everyone, even if some of the sleaze bags also make a mint in the end. Most will lose money, which goes towards the goal of impoverishing them.