Phones that only let you make phone calls and send and receive messages are often called "dumbphones". This is in contrast to Internet-enabled phones with advanced capabilities running operating systems like Android and iOS, those are called "smartphones".
I personally don't like using the term "dumb" to mean unintelligent or idiotic, and I make an effort to avoid using it that way. Similarly, I would like to find a better term then "dumbphone".