IPhone or Android?
There are a lot of reasons you could choose one over the other.
If security is most important, it's easier to check an iPhone than an Android phone.
With iPhones, make sure you are running the latest ios operating system with it's updates.
Go to settings, then general and check there.
With Androids, Data Doctors Ken Colburn says there's a new app that can tell you.
It's called Snoopsnitch.
It's free and its maker says it "analyzes your phone's firmware for installed or missing android security patches."
Snoopsnitch will let you know if there are missing updates.
It may also indicate if you have an outdated phone and need a new one.