I have a PhD. What I don't have is a high school diploma, a bachelor's degree, nor a master's degree. Due to family stuff when I was younger, I dropped out of high school in 11th grade after already starting to take courses at a local community college, then attended two other undergraduate institutions (gaining acceptance after sending community college transcripts and they never asked for HS stuff since I had 30+ credits from community college). I earned a total of 130 US credit hours before applying to grad school in the UK. I wasn't awarded a bachelors degree due to residency requirements and needing the final XX credit hours to be at the last school I attended.
I was accepted into a MSc. program in the UK since all of my transcripts combined together to be the equivalent of a BSc. (Hons) in the UK. I transitioned into a PhD program after I completed coursework and my research proposal was accepted for continuing as a PhD candidate instead of writing a MSc. thesis.
I have been working for a while as a post-doc researcher in the UK but recently started to apply for some industry positions in the US (where I'm a citizen). Many of those applications have been forms asking for all my education (high school, college, grad school, etc...).
I've been asked a few times by HR people on phone screening interviews about my high school and bachelors since I don't list any on my resume/applications (since I don't have them). I think the reason they are asking is because I'm a US citizen but only have a PhD from a UK school on my resume and my post-doc positions, so I get their curiosity.
Any advice is welcome. In case it matters: PhD is in a mechanical engineering specialty.