Block from U+1D00 to U+1D7F. This block was introduced in Unicode version 4.0 (2003). It contains 128 codepoints.
The Wikipedia provides the following information on block Phonetic Extensions:
Phonetic Extensions is a Unicode block containing phonetic characters used in the Uralic Phonetic Alphabet, Old Irish phonetic notation, the Oxford English dictionary and American dictionaries, and Americanist and Russianist phonetic notations. Its character set is continued in the following Unicode block, Phonetic Extensions Supplement.