[Angrypokstick]

Yes, you are right, to revive Johan. Pheles would have to do it at Yuji's expense. Originally Pheles planned to sacrifice Yuji to bring back Johan. However.....

Spoiler:

Her plans were surprisingly stopped by non-other than Johan himself, also if my memories serves me. another entity in the reiji maigo used the silver flame to play a part in it as well.