Why does the picture on my iphone 6 plus shrink to the lower half during you tube

@viknes.t

It seems that you rotation lock is enabled, view the link below tho assist you in disabling it

If the screen doesn't rotate on your iPhone, iPad, or iPod touch - Apple Support

Dear,viknes.t To fix this problem you must turn off portrait orientationif you turn it horizontally while watching a video you should get fullscreen. ********* Always feel free to post any more questions you have about Apple.

Thank you for using Apple Support Communities.

All the best, Evan *****

<Edited by Host>