public RankingExpressionFunction getGlobalPhase() {
        if (globalPhaseRanking != null) return globalPhaseRanking;
        return uniquelyInherited(RankProfile::getGlobalPhase, "global-phase expression").orElse(null);
    }
Returns the ranking expression to use by this. This expression must not be edited.
Returns null if no expression is set.
config-model/src/main/java/com/yahoo/schema/RankProfile.java