Most schools requires only a masters to teach undergraduate classes. However, some schools pay a bit more to adjuncts with a PhD but this has to be accredited, for a foreign school, this means an equivalence evaluation report from an institution accredited by NACES. If someone is a professional adjunct with little intention of becoming full time or tenure faculty, it doesn't make sense to spend 50K on a PhD only to get a little pay increase as an adjunct. In a competitive world, the PhD has also a weight when getting adjunct work. Many people come to the forum asking for a cheap solution to the problem of getting a PhD on an adjunct salary. A typical adjunct working at several school make somewhere between 50K to 100K so there is little room for a heavy investment on a PhD. However, the dilemma is if a school from a foreign country from a developing nation like Nicaragua, India, Malaysia, etc has some use for an adjunct in the US even if evaluated as equivalent to a US PhD. My experience tells me that most likely yes in a community college environment and a maybe in a University environment. It is also about opportunity, timing, teaching evaluations, etc, etc. It cannot hurt to get a foreign PhD with a positive evaluation from a NACES accredited credential evaluation service. The minimum requirement to teach a subject by many schools is the graduate certificate (18 credits on the teaching subject), but this is the bear minimum. This means that if a person shows up with a PhD and some publications in the subject, most likely he or she would be found more qualified than a person with a graduate certificate. There is a trend to hire PhDs for adjunct work even at community colleges, the pressure is there so the foreign PhD might be the cheapest way to get it. Again, if the goal is not to become a full time faculty and all you need is a PhD to be more competitive, the foreign route might be a feasible option provided that the school is accredited and can be recognized in the US as PhD equivalent. I have a foreign doctorate (Australia) and worked in the US as an adjunct for many years, it was quite easy to get work with a foreign doctorate but all the schools asked for the NACES equivalence. Some colleagues have degrees from Philippines, India, Malaysia and were working as adjuncts as well so the foreign route is a feasible way to become adjuncts.