The workaround, for now, is to add this custom CSS to the form builder Custom CSS field:
@media (max-width: 500px) {
.givewp-layouts-goal__stats-panel__list-item { min-width: 0; }
.givewp-layouts-goal__stats-panel__stat-value, .givewp-layouts-goal__stats-panel__stat-label { font-size: .8rem; }
}