Internal page dropped from #2 to nowhere

Hello,

A short description of my website: Promoting homepage with a few keywords + internal pages ( /iphone5, /galaxys4, /htcone ). I'm building only white hat backlinks manually a few per day, no spam at all!

Suddenly one of my internal pages after was ranking #2 got nowhere in google (i looked over in all pages), the page wasn't deindexed, all other pages kept the good rankings, the homepage as well. Instead one blog post ( /iphone5-how-cheap-will-it-get-in-time ) is still ranking for my keyword but on 5th page.

Any ideas what could have happened? Will it ever come back? Should I continue to build backlinks to that page? Thank you!

This is normal for pages that have backlinks and also not a lot of backlinks, it could be a dance from the latest algo as adjustments roll out.

Also, any link building to increase your PR and SERP position is considered black hat in the eyes of Google. No follow links are not seen as black hat if they were the kind of links you built?