Hey arnab!

Yes , it is true that DNAs are made from nucleotides , each containing a five carbon sugar  backbone , each containing a phosphate group and nitrogen base. So , it should obviously be called as bases because of nitrogen base. But it is also attached to a phosphate group , which is acidic in nature. And this acidic nature dominates the basic nature of DNA making it a Deoxyrhibo nucleic acid .

Hope i have resolved your query!