I am asking a question not an opinion thanks
OK... I understand you're hurting OP. There was a reason I asked.
IME, reading the emotionally intimate messages between my partner and the OW absolutely killed any possible chance of a reconciliation. (There were also sexually explicit messages but those bothered me much less.)
I totally understand that NEED to know, but honestly for me it was a destructive urge. The messages would not leave my mind despite my wish to stay in the relationship. We wobbled along for another year until finally the last wheel fell off and I left. It was only after leaving that I found peace.
So if the aim is to stay - I would not want, personally, to read those messages.
If the aim is to get enough evidence to make a decision on leaving, then I'd take the phone to someone experienced in mobile data recovery, along with DHs Google account details.
Unless the phone has been in your possession since the discovery, unfortunately he's had plenty of time to make sure it's fully deleted - unless he's a complete numpty.
Or go to OW directly and bluff: "I've heard what DH has to say about you. I'd like to hear your side of all this." You'd need to do this in person, unannounced, as otherwise she'll just contact him so they can get their stories aligned.