Haha wow, that's really interesting! It is quite irritating to get interrupted in the midst...
The only way I can make entire pieces, as of right now, is if they're quite structured/ repetitive. Otherwise I would certainly not be able to remember the whole thing. Also, this is one of the first times I have gone to near completion of a piece, usually its the odd phrases as you mentioned. Those are a bit annoying though, since oftentimes I don't end up using them and they fall by the wayside, lol.