Jennifer Switzer, Gabriel Marcano, Ryan Kastner, and Pat Pannuto. 2023. Junkyard Computing: Repurposing Discarded Smartphones to Minimize Carbon. In Proceedings of the 28th ACM International Conference on Architectural Support for Programming Languages and Operating Systems, Volume 2 (ASPLOS 2023). Association for Computing Machinery, New York, NY, USA, 400–412. https://doi.org/10.1145/3575693.3575710
J. Switzer, E. Siu, S. Ramesh, R. Hu, E. Zadorian and R. Kastner, "Renée: New Life for Old Phones," in IEEE Embedded Systems Letters, vol. 14, no. 3, pp. 135-138, Sept. 2022, doi: 10.1109/LES.2022.3147409. keywords: {Smart phones;Heart beat;Task analysis;Batteries;Time factors;Benchmark testing;Global warming;Green computing;mobile computing},
The repository linked above also documents the procedure to flash and setup the phones.