There is a separate article on the choice of a camera on the site, so here I will list only brief theses.
If you really want to learn how to take pictures, you need an interchangeable lens camera. A smartphone with multiple cameras is a so-so option. Smartphones are conceptually sharpened for shooting on the machine. For creativity, you need a full-fledged manual mode (at least sometimes).
You don’t have to buy expensive equipment to learn photography. Now amateur technology has developed so much that its capabilities are more than enough for advanced photographers, not to mention amateurs and beginners. You can save a lot by buying used equipment.
The main element in a camera is the lens. Buying a simpler carcass, but with a good and expensive lens is a perfectly reasonable idea.
The regular (“whale”) lens is not as bad as they write and say about it. He gets to the camera almost for free and you should not refuse him. For more information about optics, see the article on choosing a lens.
There is no point in chasing the most modern models. 
New items are always more expensive (sometimes even much more expensive), but they do not always have some kind of revolutionary improvements compared to the cameras of the previous model. Most of the time, the difference is in the details.
Frank old stuff is also not worth buying, well, except perhaps for a symbolic price.
The category of equipment that can be recommended for teaching photography can be safely attributed to all SLR and most system cameras. The main thing is to make sure that the platform is still relevant and the manufacturer has not left the market. Compact cameras (“digital cameras”) and smartphones impose a large number of restrictions and it will not be possible to learn how to photograph professionally on them.