In case you're on the market for a new phone,

The newer CPUs have 1 big, 2 normal, and 6 little cores.
Some have 2 big, and 6 little cores, as opposed to the 4 big 4 little configuration.
This means there's a potential of 6 threads a modern phone can do.

The 6 cores will be running slower per core, but overall should have about 20% more data it can process than current 4/4 Big/Little configurations on the little cores.
Current Snapdragon 600 series are pretty limited in RAM (3GB), may not have sufficient ram to run all 6 cores for boinc.
You'd have to find a phone with at least 4GB (6GB recommended).

The newer technology released this year, is based on 7nm, and next year will be 5nm.
The 5nm phones will be extremely interesting.
But phones using 7nm are still very costly today!