Those squares represent missing glyphs. The font simply doesn't have those characters in it.
Many font designers still only include the ASCII character set (256 glyphs), but it was especially common in older fonts. The problem is IPA and phonetic characters fall into Unicode glyphs usually, and there's literally thousands of glyphs in Unicode so it's very difficult and time consuming to make a full Unicode font.
So anyway TL;DR is you need another font
The only way to make that font work is to import the missing glyphs from another font yourself.