Phone Rescue by iMobie costs $49.99 for a single license. It allows you to copy all of the data from an iPhone including deleted messages which it saves as web pages so you can read them with a browser. Unfortunately the deleted messages can get pretty jumbled if they've been deleted for a long time and other stuff has been written over top of them, but I got a ton of intelligence after I confiscated my WW's phone and downloaded the contents, enough to confirm she wasn't leaving anything out in her confessions.

DS19 DS17 Married since 1990 In Recovery since 7/2017 So far so good.