the issue of 3g voice phaseout in the US came up recently in the wishlist thread and I looked up what the wider community says: npjohnson1 comments on Any T-mobile users? What phone should I get that will have a working VOLTE.
There’s a thread of US users that compared bands, but not VoLTE yet - maybe there is an update or summary to this by those users: TMobile LTE Bands & Phones for use in USA
Edit: @egx470 followed up here Phone recomendation for USA? - #13 by egx470