Is it bad to use an iphone as an e-reader for a textbook?

I rented a chemistry e-book on amazon for one of my classes but I'm not able to open it online and only allowed to read it on a kindle or in the kindle app. My mac is too old to install the kindle app so i can only read the book on my phone.

If you have Chrome, the web browser, you can download the Kindle app to that.

Ipads are great for that because its like a real book. Iphones screens are too small for reading books at least for me.