Are there any mobile equivalents of a thin client? sometimes I'd like to keep my regular phone in my pocket, providing internet and cpu-assistance via bluetoot

Are there any mobile equivalents of a thin client? sometimes I'd like to keep my regular phone in my pocket, providing internet and cpu-assistance via bluetooth, but the UI be another device altoghether. My thought for this was not for a mobile IDE, but a navigation device. iwatch is ok, but still not there.