Yes. On most smartphones, the sensor itself has a native 4:3 shape, so 4:3 uses the full sensor area and gives the highest pixel count. When you choose 1:1, 16:9, or another aspect ratio, the camera usually crops the native image, so total resolution decreases.

This is not unique to phones: most digital cameras have one native sensor aspect ratio, and other formats are cropped from it. A few cameras use oversized multi-aspect sensors, but that is uncommon.

The idea that 1:1 would always capture “more information” is the wrong comparison here. For a given pixel count or sensor area, different aspect ratios can have the same area; they just distribute it differently in width and height. What matters in your phone is the physical shape of the sensor.

As for why 4:3 is common, it is largely a practical and historical choice. Rectangular images have long been preferred for viewing and printing, and 4:3 became a common sensor format in compact and phone cameras. So the phone is optimized around its native 4:3 sensor, with other aspect ratios provided as convenience crops.