Brazilian portuguese has all the phonems spanish has, but not the other way around. half of the words have same root so brazilians understand spanish for the most part and can infer meaning.

the other way around is tougher, because what might be a “hard t” becomes a “soft t” in portuguese, a “e” sound like “i” on certain words, etc. So spanish speakers get really confused.

Just being aware of these differences can remove those “blockers” and make spanish speakers understand brazilian portuguese much more easily (since, as said before, the root of many words is the same).