That's a really interesting breakdown. I think we'll be able to build larger and larger telescopes and figure out more and more of what's in atmospheres of planets. I feel like we'll be increasingly seeing more and more life signals without it being 100% decided. I want to see articles that consider what you could see about the earth from 100 light years away with just a little bit more advanced technology than we have.

If we find a really good candidate for ET life, there are things other than interstellar probes. We'd probably start by building a much larger space telescope designed specifically for spectroscopy. The funding for a mega-scope would be easier to justify if we had a very strong extraterrestrial biosphere candidate.

There are also some literally far-out proposals to place a space telescope way out beyond the orbit of Pluto and use gravitational lensing from the Sun as a giant objective lens. It wouldn't make sense for a general purpose scope but could make sense if the exact orbit and timing were selected to observe a specific object. Difficult but probably not as hard as interstellar flight.

Phase #2 is only a thing in a strict scientific definition. Nobody will remember the decades of overt denial that life could ever exist off of earth and obstruction of exploration efforts, and handwaving away of biosignature evidence when we do finally observe life on mars, after all. Even then naysayers will claim panspermia in order to kick the can down the road further.