My question especially concerns a changing trend in vowel phonemes of American English.
Please see the Pronunciation Symbols used by the Merriam-Webster English dictionary.
http://www.merriam-webster.com/pronsymbols.html

While teaching English phonemes to my Taiwan students, I analyze and compare similarities and differences of English, Mandarin Chinese and Hokkien pronunciations.

As an interesting puzzle, you might want to figure out how I use the following data:
(4) 依近似音分組如下:
A組: [A], [e] ㄝ, [a] (大嘴ㄝ)
E組: [E], [i] (台)乙
I 組: [I], [ow] ㄠ
O組: [O], [>] ㄛ, [>i]
U組: [U], [yx], [y.]
ㄨ組: [X] ㄨ, [x] (台)有
ㄚ組: [o] ㄚ, [u] (小嘴ㄚ)
ㄜ組: [.] ㄜ, [.r] ㄦ