The US Census Bureau gathers data on educational attainment of people living in the US, broken down by race, sex, age, and other categories. They specifically include "Hispanic origin" (though they do not consider this to be a "race"). The data come from the American Community Survey and are widely considered to be authoritative.
Here is their data for 2017.
If you look in Table 1, "Educational Attainment of the Population 18 Years and Over, by Age, Sex, Race, and Hispanic Origin: 2017", in the file labeled "Hispanic (of any race)", you'll find they estimate there are 235,000 people over age 18 of Hispanic origin who have a doctoral degree.
In the "All Races" file you can find that the total population over age 18 in 2017 was 246,325,000. So of the total US adult population, about 0.095% are people of Hispanic origin with a doctoral degree; even less than Freytes-Ortiz's figure. Also note that "Doctoral degree" may include degrees other than PhD, such as EdD, DD, etc (though not MD, DDS, JD, etc, which would be under "Professional Degrees").
This file also estimates 4,096,000 people of all races with doctoral degrees. From this, I get that 1.6% of the adult US population has a PhD, and of those, 5.7% are of Hispanic origin. Pretty close to Freytes-Ortiz. She may be using data from a different year, or a different source.