You will be mostly placed with any other economic migration applicants. There will be no special treatment or direct benefits, but as a PhD student in a Canadian university, most likely you will have better language skills than most applicants from outside Canada, and we all know that high language scores will give you a lot of additional points (within the language section and the transferable skills section as well).
Also, the full-time study requirement applies only for CEC. PhD students with paid RA/TA experience can still apply, provided they provide appropriate letters of references and have at least continuous 1,560 hours within the last 10 years. PhD students, with paid TA/RA experience can easily get this many number of hours after more than two years in the program. This experience will count as an experience in Canada, so combined with high IELTS scores (CLB level 9 or 10), a PhD student can easily score in the high 400s or low 500s, which will make them highly competitive within the EE pool.