What is a good camera for amateurs?

I love taking pictures and want to invest in it a bit. Right now I use my phone, iPhone 6+ s, and I want something that will get me better quality photos. I'm a pretty fast learner but I don't want to bite off more than I can chew for my first camera.

Nikon

To really learn the fundamentals of photography, you need a fully adjustable camera like the inexpensive, refurbished Nikon D3200 (under $370 with lens).

Visit the Nikon, Pentax and Canon websites and look for entry level cameras that fit your budget.

Yes, you can use it in the "auto" mode, but it can also be controlled using the cameras lightmeter to help you get great exposures.

Any DSLR from Nikon, Pentax or Canon will be a huge improvement.
Mirrorless cameras from Sony (e.g. A6000) will be equally impressive allowing for a lot of control.