I'm not really a phone person tbh, replying to you now from mobile but that's rare for me, mostly I just use the phone apps as notification collectors.

That said, I've been terminally online since the turn of the millennium so flitting between various websites and apps and generally being a bit of a "power user" comes naturally.

I use Mastodon in advanced mode with various columns pinned with my hashtag searches in. Lemmy I stick with the default web UI because certain niche things tend not to work in the alternate frontends and I do a lot of niche stuff 😅

In terms of posting between the two, I often do post to Lemmy via Mastodon just to get the conversation from both places all happening in one thread. Works well as long as you bear the various quirks in mind, but I hope that'll be improved over time as well as asking the option to crosspost the other way round (ie Lemmy to Mastodon).

Would be happy to do a write-up on exactly how that works and what the limitations are if anyone would find it useful!

Edit: forgot to add, one of my pinned Mastodon columns actually shows posts from some of my fave-but-tiny Lemmy communities, so that way I don't miss anything.