The only possible option you have at the moment if you wish to stay with Sailfish in the US is the Sony Xperia 10 III. This has a beta version of the VoLTE functionality on it that users can enable if they want to try it out and help test it. Look here:
I don’t know whether it would be available on your service provider, but you can find the latest results of community user testing on various networks and in various countries here:
Basically at the moment its at your own risk as the VoLTE functionality on this phone is still in Beta mode.
Its also only on the Sony Xperia !0 III. Jolla have plans to bring it to the Xperia 10 II next, but nothing has been said by Jolla about VoLTE availability on any other supported phone, including the XA2 - so we may get it on this model at some point, or we may not.
And before you say anything, Yes Jolla are way behind the curve on this one and perhaps should have done something much sooner with regard to VoLTE - but we are where we are and history cannot be changed.