What sequence settings should I use to edit 4k iphone footage?

I'm editing 4k iphone footage at 60fps.

But whenever I try to move through my sequence in the timeline using the arrow keys, the cursor doesn't move forward exactly one frame or seems to get stuck on certain clips without responding.

Any ideas why this is happening? It's happened to me before and I fixed it by getting the sequence settings right. But I'm not sure what to adjust the sequence setting to in order to get things syncing properly.