Building an ARM64 laptop

> Considering ARM's lower energy use,

This world is a bit more complicated than simplistic statements like this.

The ARM ThunderX has a 100W TdP. The x86 Quark D1000 can go configured as low as 1.6mW.

> dissipating the heat generated on a high-end smart phone over the surface of a laptop might be enough to stay fan less without excessive heat?

Yes, but no one is going to underpower a laptop with the TdP of a smartphone. That would be just a waste of ability to dissipate power and limit the performance for no good reason.

If low skin temperature is more important that performance then you can just reconfigure the performance settings, no need to design crippled hardware to stay cool.