I’ve always been hesitant to host any services on a device with a non-removable battery. Having a battery constantly charging and discharging isn’t great for it and could potentially be a fire hazard. I know modern devices have gotten much smarter about how they charge, so maybe it’s not as much of an issue anymore, but still something to be aware of depending on how old your phone is or how you modify the firmware.
Personally, with how cheap you can find a mini PC or SBC, I would just save up a bit (maybe even sell the device you’re planning to host on) and keep an eye out for deals. You’re going to get a lot more freedom and power with those devices, and not have to try to hack around the limitations of a mobile OS.