I've had to fly with dozens and dozens of nasty colds with tons of upper congestion.

When I asked the doc about this, he explained that there is NO danger on ascent. The pressure from the ears releases through the phlegm and into the throat.

But on descent for landing, the passageways (in/near the throat) MUST be clear or the above described pain and damage could occur. Appropriate heavy duty decongestants can be taken 90 minutes before descent to deal with this with no guaranteed results.