The Mobian project aims to bring Debian on mobile devices. It is maintained by 2 distinct (but overlapping) teams:
the Mobian team is responsible for maintaining downstream packages (containing non-upstreamable patches and/or not ready for inclusion into Debian) and non-packaging tasks, such as image generation and distribution
the DebianOnMobile team maintains packages which are already part of the Debian archive.
Also see Mobian on pine64 wiki
Project wiki (community maintained): https://wiki.mobian.org/
IRC: #mobian on OFTC
Gitlab (deprecated as of 2022-07-08): https://gitlab.com/mobian1
For installation instructions see e.g.InstallingDebianOn/PINE64/PinePhone or the community wiki above