Johannes Ukraine is (at least for now) not a member of EEA or EU. That means if you permanently relocate to Ukraine and leave the EEA, you cannot continue using bunq. But of course as long as you continue to be a resident of any EEA country, then you can travel everywhere you want and use your card, including Ukraine. You can also change your mobile number to any number that is convenient for you.
For example I‘m a resident of Germany but I have a US phone number registered and receive all text messages without problems. But if I ever permanently leave here and go to live in a non-EEA country, even though my citizenship is also German and would continue to be so, I wouldn‘t be able to use bunq anymore.
Hope that makes it clear 😃