Siri voice output has stopped working on my iPhone

Continuing the conversation with myself :-)

Just saw this thread No Siri audio over bluetooth - Apple Community and realized it is duplicate. That gave me the hint to fiddle with bluetooth settings.

Sure enough, with an external bluetooth headset connected, the bluetooth icon displays on the Siri screen. When I tap it, I can select iPhone and Siri audio works again. If I disconnect the bluetooth headset, the bluetooth icon is no longer available (that makes sense in terms of expected user experience). However, at that point the Siri audio is not re-directed to the phone and there is no way to force it (the bluetooth choice is gone).

Clearly a bug.

I may have just solved my own problem. Tapped on the bluetooth indicator on lower right of Siri screen and noticed that phone was connected to an unused Bluetooth device. To be more precise, only Siri was connected to an unused Bluetooth device. I didn't realize there could be an independent bluetooth connection for Siri that doesn't respect the primary bluetooth setting for the phone.

This seems to have solved the problem at least with phone audio out.

I will know definitively if this solved the problem when I try again using CarPlay later this evening.

Oddly enough, it has stopped working again. Same symptom as before. Though now, when I activate Siri there is no bluetooth icon on the lower right. TBH, I'm not sure when the bluetooth icon does appear... I just happened to notice it earlier today on the Siri activation screen and tapped on it. Now, it's not there.

I'm mystified. And without Siri voice.

13.2 update fixed this for me.