I was born in Rio, and have lived here for the past 5 years (after a long hiatus). The point about iPhones/smartphones is simply not to aimlessly flash it too often/for too long when on the street (i.e. wander around for a long time with your phone at arm's length looking at maps, etc). Preferably order your uber before you leave the premises you're in (hotel, shop, restaurant, etc). If you must use the phone while out on the street, just make sure it's quick and check your surroundings first. Remember that as a tourist you may stand out a little more than your average carioca, so you'd have to be a little more conservative in your actions (I call an Uber on the street, check my instagram feed, etc although sometimes I get reminded by people that I shouldn't be unnecesarily putting myself at risk for doing so).

With regards to credit cards (and valuables in general) is to spread your risks by leaving the bulk of your cash, and credit cards in your hotel safe. Expensive watches and jewelry are not a smart thing to take to Rio, unless you will be attending a wedding or some other fancy event. Gold chains, no matter how cheap or insignificant they may seem to you are a no-no, as it's a favorite target for youths to pull off your neck on the beachfront. To be fair, the chances of you getting mugged are very small, but not entirely negligible. In reality, poorer people get mugged more often for the simple fact they live in the more violent areas of the city, as opposed to the relatively high safety of Zona Sul that you will be in.

The idea is, be careful but don't give in to paranoia. I have had many foreign frieds visiting over the last few years, and not a single one had problems of any kind.