The topic of having access to your partner's phone is really a controversial and debatable topic, I have watched and heard different individuals give their different opinion and suggestion on this subject matter and they all have made valid points.
To most persons it's bad , it's crossing and stepping on boundaries, it's considered an invasion of their privacy, to others it's acceptable, it's protecting their peace and having enough knowledge of who their partner is or doing secretly.
The fact is it's good and also not good to have access to your partners phone.
Having access to your partners phone has it pros and cons.

Personally, I will love and appreciate transparency and honesty from my partner, because I'm also a transparent and honest person.
And to be transparent to my partner also involves sharing phone password , having easy access to their phone, this is something I can do, and I also expect my partner to do same, it should be mutual. The moment my partner refuses, I begin to feel insecure and curious about what is being are hidden from me.
To some it might be a toxic trait or insecurity, but to be very honest, relationships in our society have been full of negative surprises, lies, pretense and unbearable secrets and if having access to my partners phone will make me feel safe, then I will do so, if having access to my partner's phone will save me from wasting your time , feelings and love, I don't see anything wrong in having access, a mutual access.
Secondly, How else am I suppose to build trust and feel emotionally secured with my partner, if I don't have access to their phone?
Having access to my partners phone builds trust between us, even when I have my doubts and insecurities or suspects.
Having access to my partners phone doesn't permits one to check incessantly or check some confidential chats , it's basically for emotional safety and trust.
You could check your partners phone periodically, especially when you feel something is wrong or begin to loss trust.

The third opinion I have on this subject matter is how helpful having access to your partners phone could be in times of emergency.
We live in an unpredictable world and sharing passwords to a few persons you trust , especially your partner is also good and a form of security, we can't tell when it could be useful and helpful to us.
An information or observation gotten from having access to your partner's phone could really be a helpful, I have heard stories of how people stay in total darkness about vital information and that the common act of searching their partners phone will really help and prevent them from making a mistake of ending up with the wrong person.
In conclusion, having full access to your partners phone doesn't even stop a person from hurting you or guarantees a healthy relationship or marriage, but rather having access to their phone makes them smarter in keeping secrets and hiding traces, what really stops a person from hurting their partner is respect and love.
Thanks for reading ♥️