A little back story.....

Currently on vacation with the family and my wife needed to take our daughter upstairs to the hotel while I stayed with our three boys at the pool. While in our room she couldn't find her phone so she used mine to call herself. 

She explained to me that she was unsure how exactly my phone worked (I recently changed from apple to android after 5 years of us using iOS exclusively, so I buy that she didnt know what was what to an extent).  In trying to open the 'phone' area to make a call (a picture of a phone on the front page) she instead stumbled into the text messages, scrolled a couple pages down, and found a thread between my step mom and myself. After scrolling through this for a couple of screens, she found a message from a me to my step mom where I vented a bunch of things about my wife. 

Now these are things that I would not say directly to my wife as they would both hurt her feelings and start an argument that would not go well in my favor.  Specifically, my wige was upset where I referred to her as a 'slob' and 'pack rat' in regards to the fact that she still has clothes that do not fit her from 10 years ago prior to our first son being born that she refuses to get rid of while also collecting more and more clothing. It is to the point that I had to remove all of my things from our shared dresser and closet as there was no more room. She currently has over 100 folder shirts and a full walk in closet of dresses and blousses that are hung (this number is not inflated as I'm the one that does the laundry in our relationship).  This, and other areas where she simply does not take care of her things (multiple coffee cups left in the car for weeks, etc), is point of tension in our relationship and both my wife and step mom are aware of this.

My wife is furious that I would ever speak about her behind her back like this and feels that me implying that she is a slob is insulting as she works incredibly hard to help provide for our family (which she does) and the only reason she hasn't gone through her clothes is because she is so busy with work an family (which is true. She is incredibly busy).  

I mad that she went through my phone in the first place. I dont buy that she accidentally stumbled upon something like she says she did. I feel that I should be able to speak to family about what is bothering me and if I chose to not bring  certain frustrations to my wife's attention, then so be it. 

Am I in the wrong here?  Am I the ass hole in this situation?