Here comes the next question: "for GPA, do you know if they only look at bachelors degree grades (all of them) or masters degree grades or both?". Well, I can only speculate or repeat what I've seen other people writing about the subject.
I think they look at both. But the importance they give to each one may be different, for several reasons.
First, the length of a bachelor's is different from a master's. So, a bachelor's may be able to prove more information, and its length is closer to a PhD. It will allow schools to evaluate if you are someone who does great in the beginning, but lose steam in the last years, for example.
Subjects you studied, courses you've taken may also be very different. Maybe you studied a lot of advanced math during your bachelor's, but not during master's (or vice-versa).
So, it makes sense to look at both to find evidence of strentgh or weaknesses which can show if you are a great applicant or not.
During my interview, I noticed that my master's had a great weight when professors were evaluating my profile. Since I'm an older applicant, my bachelor's degree was long ago, it only showed about my potential decades in the past. So, my undergraduate level does not tell them much about how I am nowadays. As I had also decades of professional experience, they were worried that my academic skills might be rusty. However, my master's degree is recent, I got a great GPA, and was in the top of my class in course like quantitative research, which is important to my PhD program. That's something we talked about during my interview.