The word plumeria has four syllables.
Plu as in Pluto
Mare or Mar as in Mary
Ree as in Reef
Ya or A as in Alive
The plural form is spelt plumerias.
If you hear someone start saying the word plumeria by saying plum, as in the fruit, or plum as in plumber, it’s likely they have never heard of the word and know nothing about the plant species.