Sounds like it’s not about PHOSH or even apt but an update problem in general. Anything special with your L5? It’s not still using amber or are your sources vanilla byzantium? Other updates ok - when was the last time? You have enough space (yes, probably a silly question)? And any other info you can think of for proper trouble shooting…
Maybe copy-paste or screencap some logs or apt responses?
Edit: the only previous thread that might be related to this seems to be about failed updates due to wrong time/date (clock resets if out of power) Major Issues after "OS Update" on Librem 5 - #60 by dos (scroll up and down a few messages)