It's another matter that the Church will have to settle, but as far as opinions...
I agree that a phone confession is possibly valid, but that there is still doubt involved.
Agreed that there's doubt. If any significant number of theologians hold that it's doubtful, then we must consider it doubtful. I lean toward them being valid because I haven't yet found a clear-cut principle to definitively rule it out.
So, one practical application of this is that in danger of death, where someone has no other recourse, one might attempt to call a priest and ask him to conditionally absolve over the phone. One may have recourse to doubtful Sacraments in danger of death.
Obviously this should not become some kind of ordinary way to confess and receive absolution, but it may be of use in extreme cases. I'm also thinking along the lines of a possible new lockdown some day where the churches are shut down even harder than they were last time with COVID.