Do you know the cause of this if it has only affected you the past two years? Could you try repeating common sentences perhaps so you can say parrot fashion? Try saying it in different voices. And warm up your voice, sing etc before you need to speak on the phone etc. Work out alternative words where possible for words you block…ie. If you can’t say ‘alternative’ say ‘different’ etc? Look at which letters are harder to say and divert. Would be interested to hear what others think. Good luck!