For bryophytes, an annotation indicating whether there are sporophytes present or not would be just as useful as flowering phenology is. There isn’t any issue with multiple fields since I am currently the only person recording such information in fields [Sporophytes present], but if it was made into an annotation I would probably start adding it for every observation I look at and it would also be very helpful when viewing photos.
I think it would be best to add Plant Phenology to them with just the Fruiting value available, but you could also add a new value “Sporophyte”. If Plant Phenology cannot be used without including flowering and budding, then a new annotation called Sporophytes with the lone value Present would work.