There are different kinds of phones, portables, fixes and among portables there are android/ios/windows phones smart as computers and other far more simple devices just with function to call/answer. How they are called in common language? i especially look for name of simple non-smart gadgets.
I would say they are all telephones, or simply phones.
A telephone (derived from the Greek: τῆλε, tēle, "far" and φωνή, phōnē, "voice", together meaning "distant voice"), or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user.
For the simple gadgets, I assume you mean cell phones that aren't "smart" (not the old rotary phones, for example). There are a few different terms out there, but I can't say which is the most popular. Here's a little snippet I found on this site, Back to Basics: The Best Non-Smartphones
Whether you call them basic phones, dumb phones, feature phones, or non-smartphones, this guide is going to break down some of the best options available.
The only tip I can give at this moment is to avoid "dumb phones" if you want to be formal.