Can I use the smart phone as a development board, development board and smartphones have distinction?

Android is Open Source Project (AOSP) is licensed under Apache 2.0. This is not a restrictive license like GPLv2 that requires changes be shared with the public. The Linux kernel underneath Android is mostly GPLv2 and, legally, companies are required to release modified code. In practice you may find that this isn't strictly observed and it takes some effort to a company to comply and release their GPLv2 kernel components. They may also have binary modules that aren't open source at all. You'd have to contact someone at the company to find out what their intentions are with their open source components.

Android is Open Source Project (AOSP) is licensed under Apache 2.0. This is not a restrictive license like GPLv2 that requires changes be shared with the public. The Linux kernel underneath Android is mostly GPLv2 and, legally, companies are required to release modified code. In practice you may find that this isn't strictly observed and it takes some effort to a company to comply and release their GPLv2 kernel components. They may also have binary modules that aren't open source at all. You'd have to contact someone at the company to find out what their intentions are with their open source components.