Is Cerberus capable of surviving phone flashing? If I install Cerberus on a rooted phone, will it survive flashing the phone?!!
Depends on what you flash. Living on the /system partition, it will survive a factory-reset. But flashing a new ROM would overwrite that partition and thus remove Cerberus.

If, on the other hand, you e.g. just flash GApps, Cerberus would survive – as that doesn't wipe/overwrite the /system partition.