The only solution I have found is to run an OpenVPN server at home and stay connected to it constantly. I lose a microscopically-minuscule amount of battery life, and a few percentage points of WAN throughput but it is worth it.

I then have content rules on the firewall between the OpenVPN server and the Internet.

As an added benefit, this makes the monitoring done by all cellphone providers (not just Verizon!) irrelevant because all they see is a constant, 24x7 stream of encrypted traffic to the same IP address.

As said down chat Charles Proxy is the one that I use, mostly because I've used it on macOS for years and trust the developer. It works great and has turned up SO many apps doing gross things. There are others in the store but I've never personally used them.

Charles: https://itunes.apple.com/us/app/charles-proxy/id1134218562?m...

Another that I have heard of but not used (your milage may vary and all that): Alice https://itunes.apple.com/us/app/alice-network-proxy-utility/...

You can also run a proxy on a server remotely and intercept all the network calls from your phone, something burp is common in the security industry. It's under your network settings, HTTP Proxy. It's more limited than an app like Charles that inspects all traffic but it's another option.

Not OP, but Charles Proxy came to mind: https://www.charlesproxy.com/documentation/ios/

I think it's come up here a few times, with various anecdotes about surfacing badly behaving apps.

Charles is the one I use but there are several in the App Store.