Why won't my iPhone turn on or recognise charging?

My iPhone XS that was previously working just fine one day turned off and now does not turn back on. I’ve cleaned out the charging port, however it doesn’t show the charging / low battery symbol when on charge. I have a USB voltage / current reader that monitors the current draw etc. I’m not sure if this is normal but it is being given around 5v but no current draw. If I try to power on the phone with the buttons, I get a momentary 0.3a current draw for about a second, then back to 0. I have ideas it maybe a battery issue that could be the culprit but the battery health has been pretty good. There’s no water damage and as far as I know it hasn’t even been opened. Any ideas would be helpful, cheers.