Longsheng - Fenghuang. Is it possible by bus or bus+train?

No direct train or bus runs between these two places.
So you need to take a coach from Longsheng, and go to Guilin first. Then you can take coach from Guilin Qintan Bus Station to Fenghuang Ancient City. The schedule is at 11:00 every day. It takes around 6 hours on the way. The ticket fare is CNY 160 per person.

Or you can take a train from Guilin Railway Station to get to Huaihua Railway Station. After that, take direct long-distance bus from Huaihua West Bus Station to arrive at the ancient city.