I agree with Canyouforgiveher and some of the others.
He's 12. My son is 11, doesn't have a phone, and as far as I know (!) doesn't know that word and has never used it. He doesn't do any social media, it is not necessary for a great life. He can choose to do that when he's older.
I think it is well within bounds to check your 12 year old son's phone. You're paying for the phone, he is living in your house, he's very young, yes he deserves privacy but do we really want to take a complete hands off approach when it comes to phones and social media? Things are different now, these phones are not just phones, they can access all sorts of social media and internet websites...again, he's 12, a child. Even a teen is still very young. What's with all the push on taking every bit of innocence away from children? I don't get it.
I'm in the US, and here, it is advised to allow your children access to a computer in a shared family type room where you can see the screen and supervise screen time and that would apply to a phone that can do all that a computer does. 12 is awfully young to have a phone unless absolutely necessary.
I don't like how children are expected to navigate social media/texting on their own at such a young age for the sake of "privacy." There will be plenty of time for them to be on their own. Allowing them the privacy to call girls whores is not really a noble excuse to beat down a parent for snooping.
Op, continue on being the mother to your son. I would do the same as you. What you're doing is calling parenting. If he were older, what the other posters said would apply, but he's 12.