What data is stored in the symbol table for a number token?
Typical lexers will return a sequence of pairs, where the pair consists of the token type and an optional value. For a token such as 12345, the token type will be something like "number" and the value will be 12345.  If the lexer only emitted the information that there was a numeric constant in the input, then the following phases of the parser would have no way to know which number it was, and that is obviously important.

I don't understand why you started talking about the symbol table in the end of your question, and I think you may be confused.  The quotation you gave says nothing at all about the symbol table, which usually belongs to a later phase of compilation. A symbol table maps symbols (that is, names) to values.  The quotation in your question is about tokens, not symbols.  Tokens are not usually stored in a symbol table, and there is no reason to store numbers in a symbol table.  Typically a parser will have a stack, and will push whole tokens onto the stack, and pop them off again as needed.