That's what the law says, and maybe what you believe but there is a lot of scientific evidence to the contrary.
See https://en.wikipedia.org/wiki/Predictably_Irrational and https://www.amazon.com/Influence-Psychology-Persuasion-Rober... for an oversight of (some of) the ways you can be manipulated.
Those decisions are not necessarily rational in the sense that economic theory defines economic actors that always act for their best interest.
Another great resource on the topic is https://en.wikipedia.org/wiki/Thinking,_Fast_and_Slow
Most of our decisions are not the result of conscious, deliberate thoughts. Our deliberate selves can be manipulated, but that's our instinct that's the most prone to manipulation.
Advertising is designed to make us act for the benefit of corporations, not necessarily our own benefit. It is nowadays built on the science that I've linked to, and they pour billions of dollars into it because it's so damn effective.
Speaking of phones, status symbols may have been important for survival 10,000 years ago, but they aren't anymore (or much less), and yet we still seek them, and corporations take advantage of that instinct to milk us by selling more and more useless, shiny junk. The ego boost is short-lived though because the next best thing is always around the corner, keeping us on the chronic dissatisfaction treadmill.
And I find repeating myself again: I agree with most of what you wrote, but it doesn't contradict my point in any way.