Sound quality of iphone calls

There has been an immense amount of advances in all tech aspects of Iphones up to today.

However the main reason for the Iphone's existence and use, has not been considered at all i.e telephone call sound.

Its sound quality is very poor, and ring, and line access and conversations are of very questionable quality.

Apparently this very elemental service is years behind and ever provides a distant and poor sound within the phone app.

Why has this basic service been left behind ?