The ones to watch are Gajim and Dino. Both are likely candidates for the emerging Linux phone platforms. Though neither quite there yet, there is a lot of activity across the projects.

Dino: OMEMO for one-to-one and group chats. Calls (encrypted) are in nightly builds, and there is a branch to use libhandy for the UI to make it more mobile-friendly. Some more info here: http://wiki.postmarketos.org/wiki/Dino

Gajim: The older and more mature project, it too supports OMEMO. The UI is currently being revised. Although it supports calls (and has for a long time), it doesn't yet support some of the more recent advances, including encryption for calls. This is on their roadmap. Again, postmarketOS has a dedicated page: https://wiki.postmarketos.org/wiki/Gajim

Kaidan is worth a mention as it uses Qt and aims to be mobile-friendly. However it is much younger and still has a number of rough edges and unsupported features: https://www.kaidan.im/