Is it possible to use an iPhone 6 as an dumbphone?

I'm thinking about getting an iPhone 6s Plus to use it as an iPod but also as a dumbphone to also communicate with it with Whatsapp and maybe I will also install Google Drive on it.
So I wanted to ask if it is even possible to get an iPhone 6s plus nowadays with the ability to download apps from the appstore and how secure is it to use it nowadays now that it gets, as far as I know, no updates anymore if I only use the apps and don't browse with them