When it comes to the CV format for a PhD application, it's important to strike a balance between providing detailed information about your research experience and maintaining a concise cover letter. I've not heard of a cover letter for a PhD program before, but there's nothing stopping you from including it even if its not required. Here's some guidance on how to approach this:
In your CV, you can provide a comprehensive overview of your research experience, including details about the projects you've worked on, methodologies used, key findings, and any publications or presentations resulting from your work. This section should highlight your specific contributions and showcase your expertise in the field. By providing this information in your CV, you ensure that the admissions committee can easily assess your research background and skills. Also, applying for a professional job and an academic position / PhD, I would consider reorganising my CV so the academic experience and qualifications are first, sections for papers, grants, awards might also be important to prioritise, whereas in a professional CV your work history would be the priority (depending on the job of course).
The cover letter should complement your CV and focus more on your motivations, goals, and how the specific PhD program aligns with your research interests. Rather than repeating the detailed descriptions of your research experience, you can mention the key highlights or the most impactful projects briefly, emphasizing the relevance to the PhD program you're applying to. Use the cover letter as an opportunity to convey your enthusiasm for the field, explain why you're interested in pursuing a PhD, and demonstrate how the program and research environment align with your academic and career aspirations. A lot of this may overlap with other statements that are required by the PhD application process, e.g. research statement, diversity statement, personal statement. Every PhD program can have slightly different application requirements, so be sure to customise it a little for the specific program.
By separating the detailed research experience in your CV from the broader motivations and goals in your cover letter / statements, you provide the admissions committee with a comprehensive view of your qualifications without redundancy. It also allows you to effectively utilize the limited space in the cover letter / statements to make a compelling case for your suitability for the PhD program.
Good luck with your application!