Hey there!

-Firstly, chalk out the colleges you would want to apply to based on your interests, the college's/ univerisity's ranking etc.

-Secondly, for applying to a PHD program abroad, start by looking at the admission criteria for the colleges you are planning to apply to by visiting their websites. Some colleges require you to take just the GRE general test but some might ask for GRE subject tests too, depending on the course/ research area you are planning to go for.

-Apart from that, you will also have to take English profiency tests such as IELTS and TOEFL. 

-Make sure to get in touch with your professors from your current college for recommendation letters.

-Write a strong statement of purpose.

-Additionally, make a CV, if you haven't. Most colleges don't require it but some might.

Hope this helps. All the best!