Assuming you have this finger app installed. My Android store does not seem to have one, for example.
It's just a shell function so in this case if one had a terminal app that has a shell one could add the function. No idea how feasible that is on a phone.
A terminal emulator is more heavy than a dedicated app is
I will leave writing an app to someone else. I've watched others go through all the challenges of getting into app stores and it's just not for me.
Fortunately some phones allow you to install apps, not just get them through the overpriced shit store.
Finger is a protocol. It's older than IP.
You can read about it in RFC 742.
Unix, Linux and BSD have finger built in.
Just found out macOS has it too. Created a .plan file and used finger on my user name and it showed the plan. There's no fingerd or anything listening on the port though, but it worked locally. Neat.