what is the difference between PHD1, PHD2 and PHD3

PHD1, PHD2, and PHD3 are not commonly used terms in academia. It is possible that these terms refer to different stages or levels of a PhD program in a specific institution or field, but without further context, it is difficult to provide a specific answer.

In general, a PhD (Doctor of Philosophy) is the highest academic degree awarded by universities and research institutions. It typically involves in-depth research in a specific field and the completion of a dissertation or thesis. The specific requirements and structure of a PhD program may vary depending on the institution and discipline.

If you have more specific information about PHD1, PHD2, and PHD3, I can try to provide a more accurate answer.