It is quite common that boards actually like slight overvoltage. This is last but not least to compensate for voltage drop across connectors, wiring and the PCB itself.
As an example the official PSU for Orange Pi 5 boards, while being marked as 5vdc output, in reality output around 5.3 volts.
Also cellphone chargers are not recommended since they are not designed to handle variable but constant charging loads. Also voltage very likely drops well below 5 volts under load.