Phoenix/Jean has 2 voices in Endsong: One is the fragment of the PF and the other is Jean's.
It's not the Phoenix talking or fighting with itself. It's the Phoenix that try to revive Jean and Jean fighting it, saying it's too early. It's Jean that says to Logan "she is soo much weaker now". It's Jean who said she lost herself in the WHR and forgot what she had to do. And it's Jean who receive all the love from her friends.
Notice too how "Jean's voice", at the begining when she "talks" to the PF fragement, looks like the power signature of Jean.