There are now a lot of cameras out there that have wifi antennas. You can use the antenna to transfer your photos from your camera to your phone. And if you have an Android phone, you can even use the NFC receiver on your phone and the cameras to transfer photos just by "tapping" the two together.
However, wireless transfers are not always reliable. With the iPhone, you have to go to Settings, choose the camera as the wireless modem. Then, after it's connected, you open the app from the camera maker, fire the app, choose the photos you want to transfer, hope the wireless connection doesn't disconnect, and on and on and on...
This process is really tedious, to say the least!
So, the easier, and for me, still the best way to transfer photos from your camera to your iPhone is by using Apple's new Lightning-to-SD Card Camera Reader. (Yes, that's a mouthful...) With this accessory, you can easily transfer photos from the SD card to your phone. No messing with settings, no opening up the different camera makers' applications... After you connected the card reader to your phone, just open up the Photos app on your phone and you will instantly see the photos you took. You can either select individual photos for importing or you can choose to import all.
That's it. Then, you can use any of the million photos apps that are already in your iPhone.
Words of caution though. One, only the second generation of these card readers are compatible with the iPhone (from iPhone 5 to the present). The first generation is only compatible with iPads, so, if you are using an iPhone, make sure you get the right one. How to make sure that you have the latest generation of card readers? Check at the back of the box and make sure that the product code is MJYT2AM/A. Two, you must have iOS 9, or later, in your iPhone otherwise, the phone will not recognize the accessory. If you satisfy both conditions, then, you are all set!
The Apple Lightning-to-SD Card Camera Reader is Highly Recommended.
Photos shot with an iPhone 6s+ using the iOS app VSCO