My iphone 11 pro volume is so low that i have to use speaker to hear the other caller. This is not only inconvenient but renders my iphone useless as a phone. any viable solutions here?

First, while on a call try changing the volume with the buttons on the left side of the phone. Those buttons only change the phone volume while actually on a call.

The other possibilities are a screen protector that is covering the ear hole near the top of the screen, or a hardware failure in the upper speaker.