You would have to guarantee those phones would eventually end up in the right person’s hands.
Otherwise if you sabotage 100 phones and only 30 go to your targets, even if you only detonate those 30 there are now 70 phones out there randomly floating around with enough explosives to kill some random person.
I would say an absolutist would be justified in crossing the border if they offer that land back at the end of hostilities in exchange for other concessions.
Even if Ukraine doesn’t reclaim all of their land they could offer Russia kursk for some other equal amount of Ukrainian land in any peace talks.
Otherwise if Russia refuses Ukraine is justified in keeping that land.