I would never trust VoLTE. It's a complicated beast full of compatibility issues. My phone supports VoLTE but on a recent trip through Europe it fell back to 2G for most calls.
Edit: Those were ordinary calls. For emergency calls I have zero experience. The last time I made one I had other things in mind then checking my network monitor app.
Due to the VoLTE end-ro-end encryption from your phone (UE) to the home operator, some countries (at least Sweden) will force downgrade inroaming users to circuit switched voice (2G/3G) in order to do lawful intercept (LI).
Is this done for everyone or just people under wiretap orders? I don't see why the network wouldn't be able to downgrade selectively since phones automatically fail over and the VoLTE service could simply refuse to authenticate or whatever.
It's still several years. I guess they just hope many phones of today won't be in use anymore and newer ones will have better compatibility. In practice some phones won't just work anymore, like in the original article.
In 2022, I imported a Samsung Galaxy A02 phone from Turkey, which I bought there in a retail store. It works, but could use VoLTE with Globe or SMART, and the operators' personnel provide conflicting answers as to why. Finally, they revealed the existence of a whitelist of models. But it worked with DITO, which is a 4G-only operator, but even that is not an argument for Globe and SMART to extend their whitelist.
Same for the newer POCO X4 Pro (international version) which I bought online.
Edit: Those were ordinary calls. For emergency calls I have zero experience. The last time I made one I had other things in mind then checking my network monitor app.