Looks nice! For the pics of your hammer corals, what you want to do is drop your white balance a little. Your phone automatically raised it but you don't want it that high. You want those nice, dark, contrasting tones.
Hold your camera up to the target, and click on where you want to focus. Usually, a square or circle outlines what you're focused on. You'll notice that a small light bulb or Sun icon pops up just outside of the square or circle. Put your finger on it and move it up or down, side to side, whatever, to adjust it. Makes for MUCH better pictures.