Application requirements for PhD in USA may vary depending on the university you wish to apply to. However, there are some basic requirements across all US universities as mentioned below:
Academic Transcripts
Standardised Test Scores-GRE/IELTS/TOEFL
Personal statements/Essay – describing your achievements and extra-curricular interests.
Letters of recommendation
Writing Samples-published papers, reports or articles if any. Or you may be asked to write an essay on a specific subject.
Research Statement- If required by the university you will describe your general research interest and give some idea about your future course of direction.
The application fee may vary from $100-150 plus the fee for tests.