My parents (M66) (F55) are separating and I think she’s tracking his phone?

My (F33) mum (F55) and dad (M66) have been on the verge of divorce for the better part of the last 5 years. The catalyst seems to be infidelity on my dad’s part, but I’ve never gotten a straight answer from either of them as to what happened so I don’t really know what to believe.

When this initially happened though, they told me they wanted to stay together and work it out, but didn’t actually put any work in and just made each other miserable. Mum continued to hold it over Dad’s head, and Dad continued to make bad choices. They also both dragged me into the middle of their conflict and made me the middle man/therapist, so they would fight about something and then I would get phone calls from each of them ranting about “your father said this….your mother said that..”. Mum has also asked me to go through his phone and send her screenshots of messages before, which I refused.

This all wrecked my mental health and I had to put my foot down and tell them to keep me out of it, because it was killing me. Dad respected this, but Mum continues on like she didn’t even hear me. I’ve backed off a lot from Mum as such, and I think she’s starting to get it as the volume of Dad related conversations has dropped a fair bit. But not entirely.

They are living separately as of a couple months ago when they had another big blow up, and both saying the separation is for real this time. They both live far from me and I’ve just had a baby, so they’ve been coming to visit separately. It seems to be that every time I talk to or hang out with Dad, Mum calls me straight after. She says she has no idea what he’s up to, but it’s too frequent to be a coincidence now. She also told me recently that she knows he’s been in contact with another woman, but told me not to tell Dad that she knows.

I’m pretty sure she’s either tracking his location at the least, or has full access to his phone at the most. Dad is not technologically savvy in the slightest, so he would have no idea how to find out. He’s coming to visit me soon and I feel like I should ask to have a look at his phone to see if she’s got access. But I’m also scared this will stir up drama and pull me right back into the middle of their fighting. And if Mum suddenly loses access to his phone after he’s visited me, she’s going to know I had something to do with it. I don’t know if I should just stay out of it or not.