One thing I did for speech therapy to help with secondary stuttering symptoms was carrying around a pad of paper and tallying each time you caught yourself saying umm, or doing an extended blink. The first step to stopping is being aware of every time you do it. If possible try and have friends or family help remind you if you forget to tally. Another thing I'd highly recommend is using a mirror to practice. Make phone calls looking into a mirror. Watch your face or make eye contact with yourself as you talk