The Precambrian eon is different from the Phanerozoic eon due to the fact that the fossil present from the Precambrian eon was of mostly microorganisms which are single cellular organisms.
Explanation:
The Phanerozoic eon was marked with eon which had the multi cellular organism that is the level of cellularity was enhanced by this eon due to the evolutionary course taken for the organisms. Phanerozoic eon and Precambrian eon had a vast difference of cellular level of organization found in the fossil remains of both times.
Precambrian eon had many primitive algae which existed mostly till the earliest Cambrian era only. Due to single cellularity of the organisms, the fossil of Precambrian eon was not much in abundance whereas the Phanerozoic eon had much abundant fossil remains.