Speed Up Podcasts on iPod Classic
There's no such way to do that, actually. So, you have two possibilities:


Adjust the tempo before add the podcast on your phone (using Audacity or something similar), you can have a look on this Super User post to understand how to do it.
Convert the podcast into an audiobook format. You can adjust the actual velocity of your audiobook going into "Settings > Audiobooks"


Besides that, I can't see no other way to do that, sorry.