As I said, make it a part of an emergency kit in the car. Easy peasy explanation. A clean regular phone you can hand over, loan to her at any time is the best defense against suspicion.I'm not sure why I see so many recommendations for burner phones. I prefer to use my actual phone, instead of finding some phone hidden somewhere, which could be difficult to explain if found. Install an app when you hobby, uninstall it when done. Yes there are a handful of agencies and escorts that demand that you call from a 'real' number which is a dumb requirement anyways because burner phone bought with a gift card can't really be traced. Any escort and agency I care about is ok with text apps.
To hide cash, have one credit card with eStatements your wifey doesn't know about. Use it to pay for things and disappearing cash can be explained that you used cash to buy those things.