I got Stable Diffusion running on my phone this weekend. Code is here.
Maple Diffusion is the second Stable-Diffusion-on-a-phone implementation I'm aware of (first place goes to Matt Waller), but it should be the fastest.
...at least, until someone figures out how to make this flag work.
Update (2022-11-11): liuliu shipped a full Stable Diffusion iPhone app using a similar MPSGraph-based approach: announcement, app store link. Super cool!