I use a Gore activeshell gilet if I want to windproof my chest area (not as bothered about arms). I think it’s a ‘Path’. It adds hardly any weight or bulk and can be stuffed in a pocket if you get too warm.
Like you I wear a Phantom in the winter and have moved to LS jersey plus gilet in the past couple of weeks.
I’ve also got an Endura roadie LS jersey. FS260, it may be the jetstream already mentioned above? It’s windproof but like an idiot I bought a mainly white one. It was in the sale – £25 but hardly gets used as the trails need to be dry or it gets filthy. Really good jersey though.
The missus has just got a LS Castelli Gabba to use on her road bike – a thinner windstopper. That thing is amazing….still not sure it justifies the price though!