Will I get a liquid detection warning even when charging a completely dead phone? I can't tell if my port is now dry, or if it is just too dead to give me the warning.

I never got my 12 wet and it still says it detects liquid but only when charging it...why?

Exactly what are you seeing? Do you mean completely dead as in nothing at all powers on? Or the minimal power that shows messages an otherwise dark display such as an image of a battery? Even when an iPhone goes into automatic shutdown, there's actually more energy available, but that's reserved for those messages. Are you seeing something like a low battery image along with a warning about liquid contact? This is the standard message when the battery can perform regular operations. Are you seeing some variation of this on an otherwise dark display?

The liquid detection that shuts down the charging is electronic and is supposed to be powered by the battery. The idea is to refuse any external power that might damage the charging port. And when it's at that level, it may take a while for it to power on and obviously won't for a while as long as the sensor on the charging port detects that it's still wet.

If you have any kind of wireless charging available, you might try using that since it should still work while the charging port is drying out.

When did you get it wet? It can take up to a day to dry. I am on an iPod touch 6th generation and it will not show up. Better take it safe than permanently damaging your iPhone.