If it makes you feel better I haven't even run Leste on my Pinephone(you can usualy just try out an OS by booting from the SD) but Leste requires installing U-boot to the bootloader partition which wipes the stock bootloader. I always used backupmenu on my N900(still my daily phone) and do not want to play around with flashing bootloaders right now on either phone.

I think you need to use the bootloader flash options when you read the wiki page on flasher but that is a guess, I have not tried that only flashing stock nokia firmwares and then OTA'ing to latest CSSU for correct kernel so I can load an old backupmenu backup.

I will also say that all of the options for the pinephone are very early alpha and other than testing and deving for leste you will probably not end up with a daily use phone vs stock maemo5 which still works probably at featurephone grade for me. I can make calls send SMS, play music and podcasts, and Maebble to link to my Pebble watch; I guess GPS too though OSM is not downloading new maps so I might as well use 2011 maps for Sygic if I dont have a tablet along.