Hi! I would like to visit both Zhangjiajie and fenghuang Cheng for 5 days.

Since there is such a long distance between the two places, so you are suggested to stay in ZJJ. After you visiting ZJJ National Forest Park, you can take a long-distance bus to Fenghuang from Central Bus Station, which is available from 8:30 to 17:20 and takes 1hour, CNY80.
After getting to Fenghuang Bus Station, you can take a taxi directly to the old town, which takes about CNY10.