I understand there are always exceptions, but when a partner is upset that the other is not sharing the password for a electronic device, my therapist spidey-senses start tingling. This is because secretive behaviour with phones and/or computers have often revealed, at least in my experience, to be tied to things like affairs, addiction, financial deception, or secret families in Michigan.
If you are in a healthy trusting relationship your relationship should be a healthy place of openness and discussion and not require the level of privacy that locks your spouse or partner out of personal electronic devices and online communications. Within the counselling environment, I have yet to hear a justified reason why an individual should lock their phone/computer from their partner. I have definitely heard couples give reasons for locking their phone, but