I already asked a similar question sometime ago (though that was focused on free apps) and the answers were negative, but I've done some research and it seems there could be a way.
Basically, I’m looking for apps which lock the phone, either for a specific app (I.e. “don’t use Facebook for 1 day”) or for the full phone (I.e., “don’t use any app for the whole day, except for phone calls & SMS”). On Android this is doable with Offtime. On iOS Offtime (conveniently renamed to “Offtime light”) is totally useless (it doesn’t lock anything at all).
However, on the iPhone I found two more apps which seem to be able to do what I want: Flipd and Freedom.
The app requires me to install a MDM certificate on my phone in order to allow locking. However, I don't know what a MDM certificate is, and since this is a company mobile, I cannot risk third parties to access my emails and documents. Is it safe to install the MDM certificate?
This app doesn't seem to require a MDM certificate (I can't be sure because I haven't downloaded it: it looks like there's no free trial, so before buying it I want to be sure it works). It does require a "limited VPN", though. Again, is this safe?
If both apps aren't safe, are there safe alternatives?