Here are a couple of databanks of NGSS-related phenomena that teachers from various regions of the country have put together. If you find some more, feel free to include those links in the comment section!
Georgia Science Teachers Association: GSE Phenomena Bank
San Diego Schools: #ProjectPhenomena
TJ McKenna: Phenomena for NGSS
EDUConsulting: NGSS Phenomena Resources
With the phenomena, come the assessments. Check out the NGSS Task Formats to see some ideas on how to develop NGSS-style assessments.