I've been using Miracle Grow Bloom Booster about once every 2 weeks. Although, I think I read where some might do it as frequently as once a week.

I'm using the type that mixes with water... so there is a second consideration.... you're giving your plumeria a big drink of water at the same time. In my case, mine already get water once a week when I irrigate the lawn. I'm not sure I want to give them a second drink every week.

Of course the other option is granules- a time release fertilizer. I feel like a liquid gives me more control though.

I see you're in Jax... guessing you have to bring yours in for the winter? I lived up there for 10 years... I remember how cold the winters first seemed, coming from a central FL native :)

Just follow packaging details. I wouldn't use it more than it instructs you to. Too much of something is never good...and that goes for phosphorous which can be toxic to plants in excess amounts.