When exactly we talk about different phases or levels of testing?

In Software Development Life Cycle phase, once the coding phase is

reached and unit testing is performed and passed by the development team, the

application moves to testing phase. Once the application is in testing phase, it

is subjected to different levels/phases of testing starting from Component testing

to Integration testing, System testing and finally the Acceptance testing.

So, it is important to understand, we talk of levels of testing once the Coding

phase is done and testing phase is started. Also, this is important to understand

that testing phases is part of execution phase of STLC.