The more "bands" a vocoder has, the clearer the speech will be.
If you need the "robot voice" or synth-vocal modulation effects that Vocodex is famous for, several high-quality Android apps provide similar functionality. FL Studio Mobile il vocodex android
A popular vocal processing app known for its "Talkbox" and "Big Chorus" presets that mimic classic vocoding styles. Audio Evolution Mobile Studio The more "bands" a vocoder has, the clearer