A smartphone or tablet can support real development, especially when paired with a browser IDE, remote development environment, terminal, or cloud workspace. Small websites, scripts, prototypes, documentation, and API experiments are realistic. A physical keyboard and reliable connectivity make the experience much better.
Limitations appear with large repositories, native mobile builds, complex debugging, local databases, device emulators, and long-running processes. File management and multitasking can also slow down careful work. These are workflow constraints, not proof that mobile development is impossible.
Use a phone or tablet for learning, reviews, quick fixes, and remote operations. Keep source code in version control, use secure authentication, and avoid storing secrets locally. When the project becomes substantial, move to a full development environment without losing the mobile workflow. The best setup is flexible: mobile for access, stronger environments for depth.