It should be in the option menu of electrum mobile wallet and choose private keys to backup your private keys save it somewhere but if there is no option i think there is other way you can check this someone also asking for this here
https://bitcointalk.org/index.php?topic=1754681.0But if you already had the word seeds backup you recover them into your desktop electrum wallet and you can backup your private keys there 1 by 1..
This is only thing that i know for now if you don' have any backup seeds i don't think there is other way to get your private keys.