[puts Style hat on and takes query seriously in the hope it'll help others]
Men who have visibly big thighs (or bottoms) and skinny calves are generally wearing the wrong shaped trousers.
DH suffered from this when five years of international-level sport left him with large muscley thighs straining to escape his 80s-style stonewash jeans.
Just as on women with wide hips, jeans-type trousers with straight legs, or (heaven forbid) tapered trousers will make the wide bits look wider and the thin bits thinner. Ditto pleat-front trousers like chinos. The pocket detail of jeans, all clustered just where they're tightest, is a bad look too.
Trousers with a bootleg cut, or that are wide all the way down, are much more flattering.
Gap is a brilliant source of trousers cut in this shape, and do smart-ish chinos as well if you need to do 'smart casual' rather than relaxed.
And remember that anything in the pockets of trousers will make thighs look bigger - shift wallet to jacket pocket, slim down bunch of keys, cull extraneous crap he carries 'just in case'.
And lo, I have rectified your husband's triagnle legs!
Unless, of course, I've misinterpreted and he has slim thighs and really fat ankles...