Hiii

USA is the most preferred country of the students. Well it is not mandatory to have an MS degree to apply for PhD in USA as they provide masters and PhD together, but exceptions are always there.
Few of the universities do require Masters degree but most of the universities give admission to students with Bachelors degree. But one thing is to be kept in mind that the basic eligibility is that one has to have atleast 16 years of education i.e you must have completed atleast 4 years of study after you 10+2.
Refer the following link for complete details.
https://studyabroad.careers360.com/articles/how-apply-for-phd-in-usa

Hope this helps.
Thanks!