Playing through on my Alt account without PS PLUS (REMAKE) Multiplayer?

So i was playing through on my alt account cause I want to plat the souls games again cause im a sadist. My alt account doesnt have PS Plus but when im playing i can see other players phantoms and even got to the penetrator fight and thought for a trophy i needed to use a summon sign to bring in Biorr turns out i didnt but i saw other players signs down before the boss fight. Do i need PS plus for the summoning/ Invasions? Planning on doing the other souls games aswell and wondering if plus is required or not