Letter of recommendation from online classes I am living overseas for work for the next two years and finished my masters 15 years ago. 

Now I am taking graduate courses at Oregon State U online to prepare for applying to a Phd program. 

I will have to get LORs from these professors but am unsure of the best strategy.

The country I am living in is not English speaking so I cannot take classes locally.
Assuming these are proper online courses, with proper work you turn in or at least exams, you should just email a couple of professors a month or 2 before you need the letters.  Explain the situation, briefly remind them who you are, and ask for recommendations.
They will be able to say in their letters what was covered in the course and evaluate your performance, so choose professors who you think will be most familiar with your work.  

This shouldn't be that different from a letter a professor for a class you physically attended, but who you never had much personal interaction with.  Note you probably get at least one reference from your undergraduate days, at least assuming that was reasonably recent.