Under the main PCB we find copper! Looks to be a thin form-factor vapor chamber. Obvious thermal grease as well. The grease is an interesting choice. ($ probably) Grease tends to dry-out and become less effective over time. Makes me think the true operational life of this phone might be a little less than others...

The back side of the main PCB shows some thin copper tapes, and one more small piece of graphite! I haven't pulled up the EMI lids yet, in hopes of further thermal testing, but my guess is a PMA or something under the graphite area.