I think one of the best way is to contribute to open source projects in the ecosystem.

Projects are looking for people. It can be as easy as documentation (although relevant docu is not easy) and can then go to code PRs.

Relevant portfolios are difficult, because the industries are so different. I once had an interview and I got a small challenge to do something with an blockchain api. If you have this in the portfolio it does not interest others.

But if you know what industry you want to break in then I would look at that and code something specifically.

So as you ask about Phoenix, Liveview create a component with data access. For example, a full featured list with paging and tailwind css that can handle thousands of records without bringing everything to a halt.