I thought the same thing, but the artist looks pretty young too, and apparently she knows what a phone booth is. Maybe it's a history thing? Like how everyone knows what a toga is?
i figure that most of them have seen enough old movies and tv shows to know what one is. i don't remember if i ever saw an actual phone booth in person, just nude payphones.
If they watch or read older media. I'm way too young to have ever been to a sock hop or a malt shop, but I know what they were and they were way less ubiquitous than phone booths.
The TARDIS being a police box not a phone booth is an even more antiquated thing that young people would not know about. The concept of them was fucking bizarre anyway, literally just grab someone and lock them in a little closet.
Reminds me of Frankie Boyle describing Doctor Who as fundamentally Scottish: "Old man armed with a screwdriver dragging a young woman into a phone booth".
Have any of the Doctor's "companions" ever tried to steal the TARDIS so that they could win the lottery? I mean, I'm not saying that I would, but if I did I'd do superhero stuff too to make up for it.