I have a 1 1/2" diameter lump on the bottom outside edge of my left foot across from the arch. feels like walking on a rock - ankle rolls in.?

You need to get : It examined. See a foot doc. Any lump really mandates a biopsy in my eyes. You need to differentiate a benign growth from malignant lesion. Such growths can be ganglion, synovial cyst, plantar fibroma. But for every benign lesion there is a malignant twin and so the risk reward ratio of a biopsy is the right thing to do for definitive diagnosis.

See a podiatrist: This could be any number of things. Only an exam and possible x-ray will give an idea of what it is.