you would need a batman-esque array of phones/the ability to send packets of pixels to render for that to work, which as far as I know would also require handing the phones the entire file, and a big part of blender’s recent performance gains are GPU tech together with vram increases and so on. With smaller vram amounts, if any, they’ll probably be limited to using their normal ram and CPU rendering.
When it comes to phones and blender, I think you could decrease render time through one of two methods
1… auxiliary utility. I don’t think adding a phone CPU will hold a candle to GPU or dedicated CPU rendering… but you CAN increase productivity. an app to send messages about the progress of renders and letting you view ongoing animation renders will allow you to see if a render needs to be stopped early/visualize errors, or even an app-based render manager that allows the computer to render without GUI. That would result in small but noticeable productivity improvements.
2…auxiliary functions processor. there are occasional parts of the rendering pipeline, that I believe require CPU. especially in the areas of denoising and similar. if you could let a separate PC, phone, or similar do all the denoising and functions that don’t require texture data, or post processing, I could imagine noticeable improvements, simply by letting both PC and mobile processor work at 100% on their own (semi unrelated) tasks, you could stand to offload a lot of the between-render work like masking, cryptomatte stuff, or even maybe BVH stuff? super unsure about that last one. all of this would be an impressive feat though, and gains are probably limited to 10% or so unless it’s a super fast render anyway.