Can an applicant who has 16 years of education (BS Electronics Engineering) directly apply for a PhD position in electrical engineering at US universities? Or are they only eligible for admission in masters of electrical engineering?
Anyone can apply for admission to any program with any credentials. The issue is whether the application has a reasonable chance of success.
Overall, it is very rare that applicants are allowed to bypass the usual admission requirements, but there are cases where this happens based on the unique circumstances of a particular applicant.
A well-known example in physics is John Moffat, who entered a PhD program in Cambridge without any prior education in physics following an exchange of letters with Einstein.
I personally know of two other examples (one an MD, the other a fast food worker) who were admitted into PhDs in Mathematics with no previous training in the field but after they had demonstrated suitable competences.
Personal experience in the field may replace formal academic competence for admission, but I wish to emphasize that this is extremely unusual and that not every department is open making this kind of exception. If indeed you are admitted outside of the usual requirements, expect to have to take “remedial” courses, and possibly an entire preparatory year, in order clear any condition of your admission.