See attached screenshot from https://linux.die.net/man/1/sox, showing some potential error in the documentation mapping. This is still the case here: https://sourceforge.net/p/sox/code/ci/sox-14.2.0/tree/sox.1#l912
-A -> mu-law
• -U -> a-law
Shouldn't it be the other way round?
Yes, that was wrong. I fixed it almost nine years ago, before version 14.4.0: https://sourceforge.net/p/sox/code/ci/f5af200cef7352195994ee670c35a0f348d73732/ Those options have since been removed altogether.
I have no idea how die.net can be nudged to update their version of the man page.