In the US, the graduate school application process is similar whether you’re applying for a master’s or a PhD. Both require letters of recommendation, a statement of purpose or personal statement, a resume or CV, and transcripts. Programs in the US and Canada usually also require a certain type of standardized test—often the GRE.
Outside the US, PhD programs usually also require applicants to write a research proposal, because students are expected to begin dissertation research in the first year of their PhD.