I've held both and the iPhone 6 is noticeably smaller than the Nexus 5.
Nexus 5: 137.9 x 69.2 x 8.6 mm (5.43 x 2.72 x 0.34 in)
So 63 cm^3 vs 82 cm^3 in volume, and 92.5 cm^2 vs 95.4 cm^2 in front area.
In this context, the iPhone 6 is actually smaller than the Nexus 5, by about 20%.
I've held both and they feel identical. Same vertical and horizontal dimensions and same weight. The thickness isn't even noticeable in your hand.