Why are all the mobile phones made by Samsung round? It doesn't look classy at all

Because Apple applied for a patent for rectangular rounded corners.

In the face of Apple's accusation that it infringed the "rectangular patent", Samsung quickly refuted Apple's accusation. The two sides filed lawsuits in many countries and regions, and both sides lost money in the protracted legal battle. Later, when Samsung released a new product, it specially asked its lawyer to help change the design scheme to avoid possible accusations from Apple!