I have a Kobo eReader (idk the specific model) and it has many advantages:

• Since its only purpose is reading, the battery lasts a lot more than the phone's one. I usually charge it once a week. (A side effect of the single purpose thing is that there are no notifications, so there are less distractions too).
• You can read no matter the light conditions, both in the dark and in intense light.
• The screen is larger than a phone's one, yet the eReader itself is small enough to fit most pockets.
• I have no problem reading on the phone, but some people feel that their eyesight tires more easily than on paper. Apparently eReaders fix this.
• It has an embedded offline dictionary and you can download more in other languages.

Some cons are:

• There is no dark mode, at least on my model.
• The screen, because of its being different from the phone's, is only black and white.
• To upload books I didn't buy through the Kobo store I need to connect the eReader to a computer. However, it has a lot of memory, so you can upload all the books you may want to read and you won't need to touch it for months.
• It's quite slow. Normally I don't even notice it, but it's very annoying if I want to read PDFs where I need to zoom in.
• I don't know if it's a problem of my device, but it's also slightly buggy. Again, it's not a thing I usually notice, just when I need to highlight something or take notes. It shouldn't be a problem if you use those features only once in a while, otherwise I suggest to keep close to you the phone/notebook for your annotations or to use a more comfortable device.

I hope this helps :)