How many syllables are in the word sphere?
There is technically 1 syllable. But in everyday speech, a syllable consisting of long e + r, as in sphere, is often pronounced as two syllables separated by a y-glide: sfee-yer, and in dialects that normally drop final r, it is always so pronounced: sfee-ya.
How many syllables are in the word once?
The English word once has one syllable.
The Spanish word once (English for eleven) has two syllables.