Study of phenological phases requires their precise identification, depending on the species. I attach some links to identifying phenological phases in several species, mainly in vines and apricots. Is also a scientific work on the phenology of some fruit species.
Here is a master thesis written on the apple tree phenology in relation to temperature. I hope it will give you some information. https://brage.bibsys.no/xmlui/bitstream/handle/11250/2577700/MasterBhandari2018.pdf?sequence=1&isAllowed=y