If you want a mobile-first environment where you can learn to code on your phone, Replit is a great option. It's a full-featured environment for building and deploying software in any programming language. Mobile and desktop apps let you code anywhere, anytime. Replit also has collaboration tools, AI code generation and instant environments that let you quickly set up a project and debug it. It supports a variety of programming languages and has different pricing levels, so it's good for solo developers and teams.
Codebay is another option worth a look if you're interested in Python programming. It's got interactive lessons, an AI Coding Tutor and a variety of courses, including Python Basics and Applied AI. It's got a playground with free Python challenges and an online compiler so you can practice and track your progress anywhere.