I would stay away from any VPN offering that is free. Reason is simple as everything that is “Free” automatically means the company needs to make money from you in another way. This usually means, your information.
On the iPhone you could use any VPN provider, e.g. ExpressVPN, that offers a native app.
There are also options like the recent Firefox Focus browser which “should” not reveal any private information about you.
Hope this helps.