Cell phones are notoriously slow in getting ready to take a picture unless you are already in the photo app.
Right you are. About 5 years ago I saw a very strange circular light in the sky about a mile away from my campsite in a remote area. It was glowing green and zig-zagging across the sky. No Smart phone at the time, but I did grab my new HD video camera. By the time it took to pull off the lens cap, turn it on, and let the auto focus kick in the light was gone.
Same with photographing wildlife, something darts across the trail in front of you, but before you can even get your camera ready, it's gone.