Estonian Engineer has built Google Pixel phone cluster
I recalled reading this story last year. Looks like any number of people are sorting through cellphone "trash" to build computing clusters. A team at the University of Tartu’s Institute of Computer Science has shown that obsolete mobile phones can be wired together to do the sort of heavy data processing normally reserved for expensive server farms while keeping thousands of handsets out of landfills.
Led by associate professor of pervasive computing Huber Flores, the engineers stripped the batteries from four discarded Google Nexus devices, fitted them with 3-D-printed holders, and powered them from an external source. The cluster cost about €8 (US$9.20) per phone, yet comfortably outperformed popular single-board computers such as the Raspberry Pi for image-analysis and website-hosting chores.
But as the article in The Register mentioned, you do need to extract the batteries from the cellphones and use an external power supply. No one wants a lot of potentially dangerous cellphone batteries all piled together.