Paphiopedilums - These are found in the tropical rainforests southeast Asia extending into China
Phragmipedium, - Are located in Central and Northern South America
There is a a huge cultural difference in their culture Phrags are cultured wetter and brighter than Paphs
Morphologically there are differences as well.
Phrags have long, sword-shaped leaves and Paphs have thicker, wider leaves that are held closer to the ground. No Phrags have motttled leaves, some but not all Paphs do.
The ovaries are a huge part of the classification of slippers. Paph ovaries are unilocular (one chamber), Phrag ovaries are trilocular (three chambers).
Flower structure is similar but genetically they are different and can not interbreed.
It takes some experience to be able to note the differences but a little experience goes a long way.