This article explains five ways to transfer photos from your camera to your iPhone. Instructions apply to most iPhones and modern digital cameras.
The most effective solution is based on wireless network technology.
Most modern professional or prosumer cameras now have Wi-Fi or Bluetooth radios. If you have one that does, consider services like Dropbox and Google Photos (Apple's iCloud Photo Library is also cloud-based, but requires an iPhone or Mac).
The easiest way to transfer photos from your camera to your iPhone is to use Apple’s Lightning to USB Adapter. Simply connect a USB cable to your camera and connect it to this special device. Then, connect this adapter to your iPhone’s Lightning port.