Regarding slack on phone, unless it's a work phone, I'd say delete it. If it's a work phone, filter notifications for direct mentions or channel alerts.
As for slack on computer, I did several things:
- snooze all notifications from 08:30AM to 08:00AM (because slack doesn't allow to do 24hour) - this means all channel/here won't trigger notifications and if someone is trying to talk to me, they get a slack tip asking them if they want to trigger a notification, even if I'm snoozed. I assume if something's really urgent they'll do so. Also, as someone mentioned here, the less available you seem, the less people will bother you, and if it's important, there's always a way.
- mute everything that's non-important or generates way to many messages - in large groups, almost always, there are lots of info that's not right away important, you can perfectly check it when you have the time.
- move slack over to browser - I did this for two reasons, first because it saves me RAM (hungry hungry slack) as I don't have another Chromium/Node instance running, and it also removes the red dot notification on my dock, meaning when I look at it, I won't be tempted to check slack for all the crap that constantly comes in. In the browser you have the red dot as well, but because the tab is pinned it's way less intrusive and it almost never bothers me.
All in all, you're getting paid to do your job, not to constantly reply to messages on slack, so this helps you prioritize your attention. I always remember that if something's really important people will bother you in other ways other than just slack. (I have been on-call and I stay true to this as well. When you get called, you open your computer and check what's going on. Constantly checking your phone is bad and does you way more harm than good)