I know the first 4 Phantasy Stars are more traditional in terms of an RPG, I am just not sure if I should play all 4 or focus on just 1 in particular. I don't think the first is on the eshop, is it?
Yeah, sadly the first Phantasy Star did not get as many ports. It's not available on Steam either. I'm guessing it has to do with whatever emulation technology they license. Most ports found of SMS games tend to be the arcade (shinobi). Although that is all conjecture.
Genesis Ultimate collection is the way to go. No doubt.
I'd say start with 1 or 4. Take your pick. It is best to play all games. But not necessary. Phantasy Star 1 feels kind of like pokemon (bear with me). And 4 is more like Chrono Trigger. Now don't get me wrong, your not capturing monsters. But Phantasy Star 1 is an 8-bit RPG that seems above all other 8-bit RPGs in terms of polish and complexity. The above may only make sense in my head... I don't know.
But I would say, if you like your RPGs like Pokemon, or the Mother series (NES/SNES) PS 1 might be a good starting point.
If you like Chrono Trigger or FF3 style best, go with PS4.
Realistically, most people won't get through all 4. So, it would be tough for me to say start at 1 if the payoff would be 4.
I personally prefer 1. But the other RPGs I love most are Earthbound 0/Mother and Pokemon Blue/Red. Take that for what it's worth.