Hello aspirant,

The vast majority of PhD applications are due in December or January , so if you're a Master's students or final year undergraduate you should start working on your PhD applications in early fall.

Further, if you need to apply for the admissions in Phd program, then you need to give entrance test.  you will be called for an academic doctoral interview at the university/ college. Your admission depends on how you performed at both stages of the process – the PhD entrance test & the academic doctoral interview . The university/college decides the weightage for each stage.

Further, some of the best entrance test for Phd program is as follows :

• UGC Net Exam.
• CSIR-UGC NET exam.
• Joint Graduate Entrance Examination for Biology and Interdisciplinary Life Sciences (JGEEBILS)
• DBT JRF Biotech Entrance Test.
• TIFR Graduate School Admission Entrance Test.
• ICMR JUNIOR RESEARCH FELLOWSHIPS.

further, to know more about the Phd exam, application form, etc, you can follow the below mentioned link to know more ; https://www.careers360.com/courses/ph-d-doctor-of-philosophy

I hope that this will help.