My experience with the Mk.1 300h was there was a lot of niggles with the voice activation system, connectivity continuity, & Black Screens in the first 6 months.
I had my iPhone & my Bud had a Samsung.
We had c.6 software upgrades between August 2013 & December 2013 & we suffered no issues after that.
Therefore , I conclude it is a phone issue Can you not try another phone which is a doddle to secure @ a Dealer or Phone Shop ?
Tel