Siri doesn't announce sender or read messages out loud on iPhone

Here’s a couple of things you could try:

• Check that "Announce Notifications" is turned on in your iPhone’s settings, under Settings > Notifications > Announce Notifications. 
• check under Settings > Siri & Search, make sure that Announce Messages is enabled.

I noticed Siri not responding to things as much anymore, so this is actually what worked for me, though I did end up changing it back, because I’m now use to Siri not responding to everything I say, and just do what I ask…

• Go to Setting > Siri > Siri Responses > and set SPOKEN RESPONSES to Prefer Spoken Responses

Mine was set to Automatic, but like I said, you get use to Siri just doing, and responding when actually needing to, rather than constantly providing feedback. But to each their own.

Let me know if any of those things work.