Gary, for a start the PE is not a phone. Yes it uses the Android OS but it a well modified version to help with using the e-ink side of things.
There is a thread about moving the internal sd to external and to use that you must follow the instructions exactly - even then some people are having problems.
https://www.mobileread.com/forums/sho...d.php?t=138124
May I ask what is using all the space on the internal storage? If it is books then those can be moved to external SD without problems, in fact I have several SD cards with different sets of manuals and information on them and just use the one I need when I need it.