When your Foldscope is coupled to a smartphone, using the focus ramp can be challenging. Ideally, ask someone to hold the phone while you focus on the sample. Sometimes bending the Foldscope slightly can help to get the best and sharpest image.
If you can't find someone to assist you, you could also tape your phone to the edge of a desk! Now, both hands are free to pan around and focus as you need.