Can I use my iPhone 6 to monitor an HDMI signal from a cable box or Blu-Ray player?

Hello gothamcop, 

Thanks for reaching out to the Apple Support Communities! From your post it appears that you want to use your iPhone 6 as a display when connected to a cable box or Blu-Ray player via an HDMI cable. 

If this is correct, the iPhone is only capable of mirroring to a display. This is where the content on your iPhone would be shown on the display. This article gives more information about what the Lightning Digital AV Adapter  and others can do:  About Apple Digital AV Adapters for iPhone, iPad, and iPod touch. 

You can read more about the TV and Video specs for the iPhone 6 on this site: iPhone 6 - Technical Specifications. 

If you'd like to leave a suggestion about using the iPhone as a display, you can do so on the Feedback page: Product Feedback - Apple.

All the best.