If you are refering to the 'phantom planet' in the Final fantasy: Spirits within movie, then no. That was not Jenova. FF7 and FF:Spirits within are seperate stories set in different settings and have no relation to eachother whatsoever in terms of story plot. What destroyed the Phantom planet was themselves, during their own civil war they blew their planet apart with a superweapon that they created. Killing them all. Their enraged spirits then rode a chunk of their destroyed planet to earth where the aliens angry souls wreaked havoc.