How much does my employer know?

Good morning

I recently switched roles and with it came a company iPhone. I still have my personal phone (used to be my small business number so people still call me on it), possibly phasing it out eventually.

I am curious how much my employer knows or has access to on my company phone? It is supervised by IT but curious what can they see?

My wife is worried I’m going to get an inappropriate text from a friend and then IT will see it?

Any info is appreciated