Of cause you should not be taxiing while you are driving but recently there many accidents caused by people paying attention to their smart phones instead of surroundings. This is a problem everywhere including Japan. So, don't do it.
ながら歩き
Nagara Aruki
Naraga .... it means while you are doing something else.
Arki ... it means walking
おやめください
Oyamekudasai
Please do not ...
Please do not "Nagara Aruki."