Speed for stills on iPhone

AirGraph is correct.

The speed button only applies to videos to speed up or slow down the frame rate. Stills have no frame rate (because there is only one frame) but instead they have duration (display time) that you can adjust. Less duration time = faster display.

-- Rich

Try to short your still images from default 4 seconds to may be 1…

Here you are:

https://help.apple.com/imovie/mac/10.1/

https://help.apple.com/imovie/iphone/2.2.9/

https://help.apple.com/imovie/ipad/2.2.9/

Thanks!! Got it. Pinch and reduce ..