That's actually not true, for now the main targeted devices are still Nokia N900 and Motorola Droid 4. The Pinephone is indeed a targeted device as well since it is relatively easy to get an up-to-date mainline kernel running on it, but it is not a higher priority target than the N900 or Droid 4.

Since Leste is based on Devuan (so Debian without systemd) you can bet that most applications that run on your Linux desktop will run on Leste as well, as long as it has an ARM binary compiled for it. And that's a lot of apps already As far as I know the main challenge is not getting applications to run on it however, but getting them usable on touch-input devices with (for now, generally) low resolutions.