Someone who knows more about how to/if you can do this on Android will have to answer the specifics for that; I know on iOS you can use custom voice control actions (along with default voice control phone navigation mode) to do more or less what you’re describing. I’m surprised if Android has no accessibility features that work similarly.
I don’t know if this is still the case, but I know years back iPhones were preferred by a lot of blind people just in terms of accessibility. Digging through accessibility settings, it looks like you can use Voice Control to tell it to open Lemmy, and VoiceOver to read all the text on the screen without touching it. I don’t know about the example you added to your OP, adding phrases it would need to interpret seems more like a Siri thing (which I don’t use), so I don’t know how well that plays with Voice Control.
I wouldn’t rush out to buy anything unless some Android people confirm it’s not doable. Apple does have people that know the software working at their stores, so they could tell you specifics for sure. And check that I’m not totally wrong, lol.