Hard white spots on leaves

I noticed today that several of my phals have small, hard white bumps
on the top of some leaves.  Just a few.  It's possible that they have
been that way for a while.  I only noticed it today because I decided
to put my glasses on and check for new spikes.  Without my glasses
everything looks great!

The plants look fine and are either in flower or growing spikes.

Help would be appreciated.