Where does Tesla market the idea that "all you need is the phone"? When you enable the phone as a key, it explicitly tells you to keep your keycard with you as a backup and that the phone is for convenience only.
People may primarily use their phone because it's convenient (I definitely do) but that doesn't mean Tesla marketed it that way to me.
Tesla barely markets anything. They don't do any advertising so their only real informational marketing is what is on their website and what you hear directly from Tesla employees including Musk (who often speaks out of his ass). Tesla would probably be better served to have a more defined and clearer marketing message. That would certainly help avoid the controversy about how Autopilot is or is not marketed.
As a practical matter this is reinforced as well by the need to still carry a driver's license. In principle the government could offer a secure digital ID, but it doesn't. Phone payment also isn't at 100%, so a backup credit card also still a good idea.
So it's necessary to have the ability to have a card on hand anyway, and at that point it's not much of a stretch to have a couple. Either via a phone case or whole wallet, but it's not like someone can (legally) just take their phone with them when going for a drive. Keeping the keycard along with license and credit card is still fairly minimal (phone digital wallet can consolidate a lot of fat card packs beyond those).
I guess the bigger risk is that while I always at least take my wallet with me in the car, I don't always take it with me out of my car while I always have my phone. Might be nice if Tesla had at least an option for some sort of fallback auth mechanism built into the car itself, be it keypad or biometric. The ones in phones are pretty good and are a pretty tiny item on the BOM, in a $35k+ vehicle seems like there should be room for it as an option?
Maybe that's overthinking it though, not like regular cars tend to have those either. Sometimes people just lock themselves out with regular keys too and that's that.
People may primarily use their phone because it's convenient (I definitely do) but that doesn't mean Tesla marketed it that way to me.