so ['fɔɪ.bɫ] (phoible) has a list of phonetic segments (sounds) used in all the world's languages. There's approximately 2,160 segments.
1,800 of them are in less than 1% of the world's languages.
Only 19 of them are in more than 50% of languages.
request for help
I think I can actually use phoible's database for this...
the average number of segments in a language
I downloaded the phoible database of language inventory sizes, and wrote some code to calculate the average number of segments in a language:
35.2125