I've programmed for nearly 30 years in all types of environments.  I can tell you that you don't need much. 

There are some who actually do some programming from their phones but I don't recommend it for doing something more than fixing a misspelled word or so when nothing else is available.  That said, there are those who do significant programming on phones.

Next option is a tablet.  You can do a ton of good programming on an android or iPad, especially with a bluetooth keyboard.  For mobile and especially web programming, that can be a pretty reasonable environment as the required power for programming is far less than business programming or than desktop on Windows or  Mac programming.

You can especially do great programming on something as inexpensive as a Chromebook.  You can get Microsoft Code (often called VSCode for Visual Studio Code) for a Chromebook at code.visualstudio.com.  vsCode is a seriously powerful programming environment on which you can program many web frameworks including various Python, JavaScript such as React or virtually any other JavaScript.  You can also program Microsoft .Net including C# or program using Java using Code.

Ideally, though, it would be good to have a decent laptop or desktop PC or Mac. With a good laptop you can do all the things above with less wait time and better performance from more powerful CPUs and you can do even more complicated programming using the most modern Integrated Development Environment, or IDE, such as Visual Studio, Android Studio, Eclipse, and more.

Programming is a lot of fun and there's no reason why you can't do a lot of serious development on whatever hardware you have available.  If you have more specific questions, let me know.  Or better yet, Google will be your friend.