My Siri’s voice is mute

Several things to check:

• The Mute switch on the left side of the phone above the volume buttons should be towards the screen
• Volume settings: Hold the SIDE button until Siri activates, then release it and press the VOLUME UP button
• Do not Disturb: Siri will be silent if Do not Disturb is enabled.
• Settings/Siri & Search - check the selection for Siri Voice. The default voice is the only one downloaded to your phone. If you choose a different voice you must wait for it to download over a Wi-Fi connection. so try some other voices.

It's June 27th, 2020, and I have this same problem, too. After trying ALL the other troubleshooting advice I could find, except resetting my iPhone's Settings, I found an acceptable workaround. It's not a fix, but it's a perfectly good workaround. I went to Siri's settings and under "Siri Voice" I changed the accent, and that worked. Siri is no longer mute, and my map navigation is not mute anymore, either. There are six accents, each with a male and female version. Mine was on the default American Female. I found I could change it to literally anything else and, after it downloaded while on wifi, all the mute problems went away. If I switch back to the default American Female again, however, the mute problems still exist. So for now I'm using British Female.

One thing that I didn’t know when I posted those suggestions; there is a known problem on the server end that affects some phones and that can cause loss of the American Female voice; it has to be fixed at the Apple end, and they are working on it.

Yeah, this works to fix Siri, but it seems this problem has taken out the voice navigation in maps as well. Switching to another voice or accent fixes Siri, but doesn't restore voice navigation in maps. I've had to switch to Waze the past few days for navigation until they fix this.