Maybe I can offer some insight from a husband’s perspective. My wife gets on my case and is “triggered” (as she has stated) by many things about me. Some of it is behavioral, as you described, but a lot of what my wife complains about it is physical or immutable characteristics about me (how I breathe, body hair, etc.). She can also be impatient with me when she has to repeat herself, just like what your husband does.
When you love someone, you tolerate some level of nagging, because one or two complaints aren’t a big deal. However, over time, these things aggregate and really wear on a person.
It’s good that you recognize when you or your husband get triggered by the other. I think it’s important to recognize each time you do it and not to let each annoyance turn into disgust or resentment. For a lot of triggers, the person who is triggered can be the intolerant or unreasonable one. For others, a behavior or trait is legitimately annoying or negative and does warrant a reaction. I think you should evaluate which triggers are your problem and which are his. My wife recognizes when a number of her triggers are her issues and not issues with me (i.e. I’m not doing something wrong by breathing) and we’re working on this in counseling.
Personally, I would get annoyed at a partner on her phone too much too, and I’ve certainly been guilty of it in the past. But it’s better to ask your partner amicably to put the phone away for a bit and explain your reasoning instead of snapping. That will only breed more resentment for both of you.
Good luck. I certainly understand your situation and also your husband’s, being on the receiving end of these triggers.