Phoenix Bookstore is opposite Gupeng Building. It was the original Xinhua Bookstore, and now it should be regarded as the largest bookstore. There is Haitian Bookstore under Pengcheng Square. These are bigger.
As for the bookstores like Huaihai East Road you mentioned, they are all foreign language bookstores of Xinhua Bookstore (there are none now), and the rest of the textbooks are generally available next to the university.
I don't know if you want to go to primary and secondary schools or universities, so it's not recommended. In fact, you can get all the basic information you need by going to the first three bookstores.
Don't use the map. There is no bookstore on Huaihai East Road. Go straight to the intersection of Huaihai West Road and Zhongshan Road. That's the new Xinhua Bookstore.