The national parks have an article with 10 tips for respecting wildlife: www.npca.org/articles/1267-10-tips-to-respect-wildlife-stay-safe-and-avoid-internet-ridicule?utm_source=parknotes&utm_medium=email&utm_campaign=blog
When photographing wildlife, it is good to understand animal behavior. It is also wise to have a telephoto lens. Yes, they can be pricey, but they are worth the investment in order to keep the animals and yourself safe.
A cell phone does not have a good telephoto lens. You can buy an aftermarket lens attachment if you do not want to carry a camera with telephoto lens. Olloclip is one option: https://www.olloclip.com/shop/lenses/iphone6-telephoto/
If you have a dSLR, you can get a decent telephoto lens for it. You do not need a professional lens to get in closer. I have the Tamron 70-300. That lens on a 1.6 crop sensor (I have the Canon 50D, but this will work on a Rebel, as well) gives you an equivalent to 480 mm. For under $1000, you can have a nice set for wildlife photography. No, it is not a fast lens, but it is far better than a cell phone for wildlife photos and it is quite sufficient for those on a budget. Just learn your limitations and work within them. Heck you may even be able to use the limitations to your advantage.
I captured the image below with the Canon 50D and the Tamron 70-300, zoomed in to 209mm (on the 1.6 crop, the zoom was the equivalent to 335 mm). Had I wanted to single out an individual bison, I could have zoomed in even closer.
So, enjoy the parks, capture images at the parks, and be safe!