I don't have any idea of how conplicated it would be, but a phone app would be a nice option. The stock dialer that comes with FOSS ROMs is OK functionally, but visually looks like it was from 2010. Plus it's not available through F-droid or other open source app store. Koler is the only serious dialer alternative I've seen, and while it looks nice it has always been super buggy.
I'm thinking of this too. I heard there's only one good alternative dialer app (don't remember if it was Koler or not). We have a lot of FOSS SMS apps but no dialer ones for some reason
I tried it back when it was under the simple tools developer. I couldn't get in to his apps (aside from the calendar) for some reason. They all felt half-baked. It's nice to see that the fossify forks are getting some love, I'll check it out again.
I like the fossify forks much better than the simple tools, I used to only use the gallery (and even for that I switched to Aves) now I have many of them as default.
Dialer is nice, though the integration could flow better.
I've tried it, but I am a little picky about UI personally. It functioned well while I used it, but had a very dated style. Totally a cosmetic issue though.