iphone app design screen size

Pixels

When working on a design for iOS, work in either an artboard of 750 x 1334 (@2x) pixels or 375 x 667 (@1x). When you use Sketch you can also export to higher or lower resolutions. That's why it is OK to work in the lower resolutions of iOS. See image below.

Points are just a tool to help with different resolutions, as you will read down below.

There's a downside to working on a @2x or @3x. When you scale down, you might have 'half pixels'. For example, if you have text that's 17px in size and you scale it down to @1x, you get 8,5px. Be cautious of that.

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Points

Check out this answer on another similar question on UX Stack Exchange.

A pixel on iOS is the full resolution of the device, which means if I have an image that is 100x100 pixels in length, then the phone will render it 100x100 pixels on a standard non-retina device. However, because newer iPhones have a quadrupled pixel density, that same image will render at 100x100 pixels, but look half that size. The iOS engineers solved this a long time ago (way back in OS X with Quartz) when they introduced Core Graphics' point system. A point is a standard length equivalent to 1x1 pixels on a non-retina device, and 2x2 pixels on a retina device. That way, your 100x100 image will render twice the size on a retina device and basically normalize what the user sees.

Source: What is pixel and points in iPhone?