Let's measure the size of Pixelworks IC. It's about 5mm x 5mm (0.2inch x 0.2 inch)
From Pixelworks CEO comment, we know ASUS ZenPad S8 use IRIS1 chip. Although IRIS1 chip also target on smartphone market, we didn't find any smartphone use IRIS1 chip yet.
When I ask ASUS tablet PM about the possibility of IRIS1 on smartphone, he imply the power consumption level of IRIS1 may not reach smartphone requirement. It will be more reasonable to see IRIS1 on tablet or laptop.