Q: mass delete all videos from Iphone

Howdy sirhawkeye64,

Welcome to Apple Support Communities.

From what I gather, you would like to know how to quickly delete videos from your iPhone 6 with iTunes or on the device itself. You can change the content that's synced to your iPhone with iTunes as shown in this article:

Sync your iPhone, iPad, or iPod touch with iTunes using USB - Apple Support

Also, the article below which outlines the process for deleting entire seasons of TV shows or individual videos on an iOS device. 

Delete music, movies, apps, and other content from your iPhone, iPad, or iPod touch - Apple Support

Delete movies, TV shows and music videos

Remove movies, TV shows, and other videos from the Videos app.

Remove movies, entire TV show seasons, or music videos

Tap Edit, then tap   in the upper-left corner of the season, music video, or movie that you want to delete. When you're done, tap Done.

Remove individual TV show episodes

Find the episode that you want to delete. Swipe left on the episode, and tap Delete.

So long.