I find it depends on the exhibit the animal is in. Getting good penguin photos can be easy in some exhibits, but in some glass-fronted exhibits the water droplets on the glass can make photography more difficult. Likewise, a lot of species can be great to photograph in some exhibits, but in other exhibits the lighting can make things a lot more difficult.
It also depends on your camera. My camera does very bad under low lighting, while my phone does horrible whenever you need to zoom. So while I've gotten good photos using both, there are circumstances where only one or the other could yield a photograph.
It also depends on your camera. My camera does very bad under low lighting, while my phone does horrible whenever you need to zoom. So while I've gotten good photos using both, there are circumstances where only one or the other could yield a photograph.