Part of the problem is that Sony has been unable to gain any traction in the U.S. where it owns just a 1% market share. In it's home country of Japan, Sony's market share in smartphones amounts to just 17.5%. Another issue affecting Sony is the company's difficulties profiting from a mid-range line, since it is getting squeezed by low-cost Chinese producers.
The company's high-end Sony Xperia Z5 series has received some interest, especially the Xperia Z5 Premium. This is the first smartphone to offer a 4K 2160 x 3840 resolution (although only media is rendered in 4K, other times the screen has a 1080 x 1920 FHD resolution). But without a strong U.S. carrier partner, it remains to be seen whether Sony can turn the business around. And if the company doesn't turn things around soon, the Xperia name could end up being one for the history books.