I am using the iPhone 6s and I shot some slow mo footage.
I then added the high frame rate clips to the time line however they are all stuck on the slowest setting And the speed is greyed out.
i have restarted the phone and created new projects to no avail.
You're not doing anything wrong. This is the intended behavior. At this time Clip does not allow you to edit the speed of slow-mo clips.
If this is a feature you'd like to see added feel free to start a new discussion thread on the forum.
please add a link to the feature request URL
For feature requests for Premiere Clip, you can either post a new thread (just like you posted this one), or tap "Give us Feedback" within the app menu (tap the product icon in the top left corner of the app and tap 'Give us Feedback').
Let me know if that helps.