You could, the solution requires math though. You need to calculate the size of the battery to be large enough to power your sever (in this case, the phone battery would need to be large enough to power whatever you side load or run within a vm on it) for a significant portion of time which you’d want to base upon the calculation of how much light per day your solar panel is receiving on average, accounting for cloudy days, bad conditions, winter, etc… Essentially what I’m getting to is that where there’s a will, there’s a way, but it likely ain’t going to be easy unless you can already find a YouTube tutorial of someone doing it.